EP4301821A1

EP4301821A1 - Set of processing fluid and inks, image forming method, and image forming apparatus

Info

Publication number: EP4301821A1
Application number: EP22707880.5A
Authority: EP
Inventors: Risa Tamura; Sei Yamamoto; Tomohiro Nakagawa; Kazuhiko Umemura; Hiroki Hagiwara; Yuya Hirokawa; Takuya Saiga
Original assignee: Ricoh Co Ltd
Current assignee: Ricoh Co Ltd
Priority date: 2021-03-04
Filing date: 2022-02-24
Publication date: 2024-01-10
Also published as: WO2022185157A1

Abstract

Provided is a set of a processing fluid and inks, including a processing fluid containing a flocculant, a non-white ink containing a coloring material other than a white color, and a white ink containing a white coloring material. When a 1% by volume aqueous solution obtained by diluting the white ink with water and a 1% by mass calcium acetate aqueous solution are mixed with each other, a rate of initial increase of a particle diameter from start of mixing until after 20 seconds is 30 nm/second or greater.

Description

[DESCRIPTION]

[Title of Invention]

SET OF PROCESSING FLUID AND INKS, IMAGE FORMING METHOD, AND IMAGE FORMING APPARATUS [Technical Field]

[0001]

The present disclosure relates to a set of a processing fluid and inks, an image forming method, and an image forming apparatus.

[Background Art]

[0002]

In recent years, commercial printing and industrial printing fields, in which analog printing techniques such as offset printing and flexographic printing have been the mainstream, also have increasing needs for inkjet printers as a means for digital printing that can print various kinds of designs in small lots without plates.

In the commercial printing, main printing items are pamphlets, catalogs, posters, and manuals. In the industrial printing, main printing items are labels, packages, textiles, and cardboard. Particularly, in the industrial printing fields, various kinds of designs in small lots are preferred and used for product sales promotion.

Examples of such various kinds in small lots include, but are not limited to, package printing for foods and daily necessities printed on nonabsorbable print media such as plastic films. In the package printing, printed matters need a very high image quality because most of the printed matters on packages are seen at close range.

In industrial printing fields such as soft packaging for foods, back printing is employed from the viewpoints of improving printing quality and preventing wear and staining of the printed surfaces. In the back printing, white inks are printed on color inks (for example, see PTL 1). [Citation List]

[Patent Literature]

[0003]

[PTL 1]

Japanese Unexamined Patent Application Publication No. 2019-156995 [Summary of Invention]

[Technical Problem]

[0004]

The present disclosure has an object to provide a set of a processing fluid and inks that can provide a clear image with little color bleed.

[Solution to Problem]

[0005]

According to an aspect of the present disclosure, a set of a processing fluid and inks includes a processing fluid containing a flocculant, a non-white ink containing a coloring material other than a white color, and a white ink containing a white coloring material. When a 1 % by volume aqueous solution obtained by diluting the white ink with water and a 1% by mass calcium acetate aqueous solution are mixed with each other, a rate of initial increase of a particle diameter from start of mixing until after 20 seconds is 30 nm/second or greater. [Advantageous Effects of Invention]

[0006]

The present disclosure can provide a set of a processing fluid and inks that can provide a clear image without little color bleed.

[Brief Description of Drawings]

[0007]

The accompanying drawings are intended to depict example embodiments of the present invention and should not be interpreted to limit the scope thereof. The accompanying drawings are not to be considered as drawn to scale unless explicitly noted. Also, identical or similar reference numerals designate identical or similar components throughout the several views.

[0008]

[FIG. 1]

FIG. 1 is a schematic view illustrating an example of an image forming apparatus of the present disclosure.

[FIG. 2]

FIG. 2 is a schematic view illustrating an example of a chart used for forming an image in Examples and including a solid image of a non-white ink in a solid image of a white ink. [Description of Embodiments]

[0009]

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

In describing embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this specification is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that have a similar function, operate in a similar manner, and achieve a similar result.

[0010]

(Set of processing fluid and inks)

The set of a processing fluid and inks of the present disclosure includes a processing fluid containing a flocculant, a non- white ink containing a coloring material other than a white color, and a white ink containing a white coloring material. When a 1% by volume aqueous solution obtained by diluting the white ink with water and a 1% by mass calcium acetate aqueous solution are mixed with each other, a rate of initial increase of a particle diameter from start of mixing until after 20 seconds is 30 nm/second or greater. [0011]

According to existing printing techniques using a back printing process in which a printed matter is seen from the back side, there are problems that a white ink and a color ink may bleed depending on the combination of the inks, or there occurs a so-called cissing phenomenon that a white ink does not sufficiently wet and spread over a color ink when the white ink is applied on the color ink.

[0012]

According to the present disclosure, when a 1% by volume aqueous solution obtained by diluting the white ink with water and a 1% by mass calcium acetate aqueous solution are mixed with each other, the rate of initial increase of the particle diameter from the start of mixing until after 20 seconds is 30 nm/second or greater. Because of this effect, the present disclosure can obtain a clear image with little color bleed. This is because the white ink aggregates at a high speed through a reaction with a multivalent metal salt, which is the flocculant contained in the processing fluid, and can be prevented from fluidizing on a non permeating print medium and can be fixed before color bleed occurs.

[0013]

When a 1% by volume aqueous solution obtained by diluting the white ink with water and a 1% by mass calcium acetate aqueous solution are mixed with each other, the rate of initial increase of the particle diameter from the start of mixing until after 20 seconds is 30 nm/second or greater, preferably 33 nm/second or greater, and preferably 70 nm/second or less in terms of storage stability.

The 1% by volume aqueous solution obtained by diluting the white ink with water is prepared by adding water (99 mL) to the white ink (1 mL).

The rate of initial increase of the particle diameter can be obtained by previously measuring the particle diameter of a 1% by volume aqueous solution obtained by diluting the white ink with water, and subsequently measuring, over time, the particle diameter of a resultant obtained by mixing a 1% by mass calcium acetate aqueous solution with the 1% by volume white ink aqueous solution. Specifically, the 1% by mass calcium acetate aqueous solution (0.5 mL) is mixed with the 1% by volume white ink aqueous solution (4 mL), and the rate of initial increase of the particle diameter is measured from the start of mixing until after 20 seconds. The particle diameter is measured by, for example, a cumulant method using a particle diameter measuring system (available from Otsuka Electronics Co., Ltd., ELSZ- 1000S). The 1% by volume white ink aqueous solution and the 1% by mass calcium acetate aqueous solution are mixed with each other, the particle diameter of the resultant is measured by a cumulant method at intervals of some seconds from the start of mixing, the particle diameter data are plotted to draw a straight line, and the rate of initial increase of the particle diameter (nm/second) can be calculated based on the slope of the linear approximation from the start of mixing (0 seconds) until after 20 seconds.

[0014] It is possible to adjust the rate of initial increase of the particle diameter of the white ink based on the constituent components contained in the white ink. For example, by increasing the amount of a dispersant contained in a pigment dispersion liquid and a resin dispersion liquid, it is possible to improve the reactivity with calcium acetate to be mixed with the dispersion liquid, and increase the rate of initial increase of the particle diameter. It is also possible to adjust the rate of initial increase of the particle diameter based on the kind of the dispersant. By using a dispersant containing many anionic functional groups such as a hydroxyl group, it is possible to increase the rate of initial increase of the particle diameter. It is possible to use two or more kinds of dispersants in combination. By adjusting the mix proportion of the dispersants, it is possible to produce a white ink having a desired rate of initial increase of the particle diameter.

In terms of improving the rate of initial increase of the particle diameter, the content of the dispersant is preferably 5% by mass or greater but 11% by mass or less and particularly preferably 7% by mass or greater but 11% by mass or less.

[0015]

The white ink contains water, a coloring material, an organic solvent, and a surfactant, and further contains other components as needed.

[0016]

<< Organic solvent>>

There is no specific limitation on the type of the organic solvent. For example, water-soluble organic solvents are suitable. Specific examples thereof include, but are not limited to, polyols, ethers such as polyol alkylethers and polyol arylethers, nitrogen-containing heterocyclic compounds, amides, amines, and sulfur-containing compounds.

[0017]

Examples of polyols include, but are not limited to, polyols such as ethylene glycol, diethylene glycol, 1,2-propanediol, 1,3 -propanediol, 1,2-butanediol, 1,3-butanediol, 1,4- butanediol, 2,3-butanediol, 3 -methyl- 1,3 -butane diol, 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- 1,3-pentanediol, and petri ol.

Examples of polyol alkylethers include, but are not limited to, ethylene glycol monoethylether, ethylene glycol monobutylether, diethylene glycol monomethylether, diethylene glycol monoethylether, diethylene glycol monobutylether, tetraethylene glycol monomethylether, and propylene glycol monoethylether.

Examples of polyol arylethers include, but are not limited to, ethylene glycol monophenylether and ethylene glycol monobenzylether. Examples of nitrogen-containing heterocyclic compounds include, but are not limited to, 2- pyrolidone, N-methyl-2-pyrolidone, N-hydroxyethyl-2-pyrolidone, l,3-dimethyl-2- imidazolidinone, e-caprolactam, and g-butyrolactone.

Examples of amides include, but are not limited to, formamide, N-methylformamide, N,N- dimethylformamide, 3-methoxy-N,N-dimethyl propionamide, and 3-butoxy-N,N-dimethyl propionamide.

Examples of amines include, but are not limited to, monoethanolamine, diethanolamine, and triethylamine.

Examples of sulfur-containing compounds include, but are not limited to, dimethyl sulfoxide, sulfolane, and thiodi ethanol.

Examples of other organic solvents include, but are not limited to, propylene carbonate, and ethylene carbonate.

Since the water-soluble organic solvent serves as a humectant and also imparts a good drying property, it is preferable to use an organic solvent having a boiling point of 250 degrees C or lower.

[0018]

The proportion of the organic solvent in the white ink has no particular limit and can be suitably selected to suit a particular application. In terms of the drying property and discharging reliability of the white ink, the proportion is preferably from 10 to 60 percent by mass and more preferably from 20 to 60 percent by mass.

[0019]

<<Water>>

As the water, for example, pure water such as ion-exchanged water, ultrafiltrated water, reverse osmotic water, and distilled water, or ultrapure water can be used.

The proportion of water in the ink has no particular limit and can be suitably selected to suit to a particular application. In terms of the drying property and discharging reliability of the ink, the proportion is preferably from 10 to 90 percent by mass and more preferably from 20 to 60 percent by mass.

[0020]

<<Coloring material>>

The coloring material has no particular limit so long as the coloring material is a white coloring material. Pigments and dyes are suitable.

Examples of the white coloring material include, but are not limited to, titanium oxide, iron oxide, calcium carbonate, barium sulfate, and aluminum hydroxide. In addition, resin hollow particles and inorganic hollow particles can also be used.

The proportion of the coloring material in the white ink is preferably from 0.1 to 15 percent by mass and more preferably from 1 to 10 percent by mass in terms of enhancement of image density, fixability, and discharging stability.

[0021] To obtain the white ink, the pigment is dispersed by, for example, preparing a self-dispersible pigment by introducing a hydrophilic functional group into the pigment, coating the surface of the pigment with resin, or using a dispersant.

To prepare a self-dispersible pigment by introducing a hydrophilic functional group into a pigment, for example, it is possible to add a functional group such as sulfone group and carboxyl group to the pigment (e.g., carbon) to disperse the pigment in water.

To coat the surface of the pigment with resin, the pigment is encapsulated by microcapsules to make the pigment dispersible in water. This can be referred to as a resin-coated pigment. In this case, the pigment to be added to the white ink is not necessarily wholly coated with resin. Pigments partially or wholly uncovered with resin may be dispersed in the white ink unless the pigments have an adverse impact.

To use a dispersant, for example, a known dispersant of a small molecular weight type or a high molecular weight type represented by a surfactant is used to disperse the pigments in ink. As the dispersant, it is possible to use, for example, anionic surfactants, cationic surfactants, nonionic surfactants, amphoteric surfactants, etc. depending on the pigments.

Also, a nonionic surfactant (RT-100, manufactured by TAKEMOTO OIL & FAT CO., LTD.) and a formalin condensate of naphthalene sodium sulfonate are suitable as dispersants.

These dispersants can be used alone or in combination.

[0022]

-Pigment dispersion-

The white ink can be obtained by mixing a pigment with materials such as water and organic solvent. It is also possible to mix a pigment with water, a dispersant, etc., first to prepare a pigment dispersion and thereafter mix the pigment dispersion with materials such as water and organic solvent to manufacture the white ink.

The pigment dispersion is obtained by mixing and dispersing water, pigment, pigment dispersant, and other optional components and adjusting the particle size. It is good to use a dispersing device for dispersion.

The particle diameter of the pigment in the pigment dispersion has no particular limit. For example, the maximum frequency in the maximum number conversion is preferably from 20 to 500 nm and more preferably from 20 to 150 nm to improve dispersion stability of the pigment and ameliorate the discharging stability and image quality such as image density.

The particle diameter of the pigment can be measured using a particle size analyzer (Nanotrac Wave-UT 151, manufactured by MicrotracBEL Corp).

In addition, the proportion of the pigment in the pigment dispersion is not particularly limited and can be suitably selected to suit a particular application. In terms of improving discharging stability and image density, the content is preferably from 0.1 to 50 percent by mass and more preferably from 0.1 to 30 percent by mass.

During the production, coarse particles are optionally filtered off from the pigment dispersion with a filter, a centrifuge, etc. preferably followed by degassing.

[0023] <<Surfactant>>

It is preferable that the white ink contain a silicone surfactant as a surfactant.

The silicone surfactant is not particularly limited and may be appropriately selected depending on the intended purpose. Examples of the silicone surfactant include, but are not limited to, BYK-333, BYK-378, BYK-307, and BYK-3450 (all available from BYK Chemie Japan Co., Ltd.), KF-351 (available from Shin-Etsu Chemical Co., Ltd.), WET-260, WET- 270, and WET-280 (available from Evonik Industries AG), and SAG503A, SAG016, SAG008, and PD-502 (available from Nissin Chemical Co., Ltd.).

[0024]

The white ink may contain any of the surfactants described below in combination as any other surfactant.

Examples of the any other surfactant include, but are not limited to, fluorosurfactants, amphoteric surfactants, nonionic surfactants, and anionic surfactants.

Specific examples of the fluoro surfactants include, but are not limited to, perfluoroalkyl sulfonic acid compounds, perfluoroalkyl carboxylic acid compounds, perfluoroalkyl phosphoric acid ester compounds, adducts of perfluoroalkyl ethylene oxide, and polyoxyalkylene ether polymer compounds having a perfluoroalkyl ether group in its side chain. These are particularly preferable because they do not foam easily. Specific examples of the perfluoroalkyl sulfonic acid compounds include, but are not limited to, perfluoroalkyl sulfonic acid and salts of perfluoroalkyl sulfonic acid. Specific examples of the perfluoroalkyl carboxylic acid compounds include, but are not limited to, perfluoroalkyl carboxylic acid and salts of perfluoroalkyl carboxylic acid. Specific examples of the polyoxyalkylene ether polymer compounds having a perfluoroalkyl ether group in its side chain include, but are not limited to, sulfuric acid ester salts of polyoxyalkylene ether polymer having a perfluoroalkyl ether group in its side chain and salts of polyoxyalkylene ether polymers having a perfluoroalkyl ether group in its side chain. Counter ions of salts in these fluorine-based surfactants are, for example, Li, Na, K, LL, NH3CH2CH2OH,

Specific examples of the amphoteric surfactants include, but are not limited to, lauryl aminopropionic acid salts, lauryl dimethyl betaine, stearyl dimethyl betaine, and lauryl dihydroxyethyl betaine.

Specific examples of the nonionic surfactants include, but are not limited to, polyoxyethylene alkyl phenyl ethers, polyoxyethylene alkyl esters, polyoxyethylene alkyl amines, polyoxyethylene alkyl amides, polyoxyethylene propylene block polymers, sorbitan aliphatic acid esters, polyoxyethylene sorbitan aliphatic acid esters, and adducts of acetylene alcohol with ethylene oxides, etc.

Specific examples of the anionic surfactants include, but are not limited to, polyoxyethylene alkyl ether acetates, dodecyl benzene sulfonates, laurates, and polyoxyethylene alkyl ether sulfates. These any other surfactants can be used alone or in combination.

[0026]

<<Resin>>

The type of the resin contained in the white ink has no particular limit and can be suitably selected to suit to a particular application. Specific examples thereof include, but are not limited to, urethane resins, polyester resins, acrylic -based resins, vinyl acetate-based resins, styrene-based resins, butadiene-based resins, styrene-butadiene-based resins, vinylchloride- based resins, acrylic styrene -based resins, and acrylic silicone-based resins.

Particles of such resins may be also used. It is possible to mix a resin emulsion in which the resin particles are dispersed in water serving as a dispersion medium with materials such as a coloring agent and an organic solvent to obtain ink. The resin particle can be synthesized or is available on the market. It is possible to synthesize the resin particle or obtain from market. These can be used alone or in combination of the resin particles.

[0027]

The volume average particle diameter of the resin particle is not particularly limited and can be suitably selected to suit to a particular application. The volume average particle diameter is preferably from 10 to 1,000 nm, more preferably from 10 to 200 nm, and furthermore preferably from 10 to 100 nm to obtain good fixability and image hardness.

The volume average particle diameter can be measured by using a particle size analyzer (Nanotrac Wave-UT151, manufactured by MicrotracBEL Corp.).

[0028]

The proportion of the resin is not particularly limited and can be suitably selected to suit to a particular application. In terms of fixability and storage stability of the white ink, it is preferably from 1 to 30 percent by mass and more preferably from 5 to 20 percent by mass to the total content of the white ink.

[0029]

As the resin particles, appropriately synthesized products may be used or commercially available products may be used.

Examples of the commercially available resin particles include, but are not limited to, MICROGEL E-1002 and E-5002 (styrene-acrylic-based resin particles, available from Nippon Paint Co., Ltd.), BONCOAT 4001 (acrylic -based resin particles, available from DIC Corporation), BONCOAT 5454 (styrene-acrylic -based resin particles, available from DIC Corporation), SAE-1014 (styrene-acrylic -based resin particles, available from Zeon Corporation), SAIVINOL SK-200 (acrylic -based resin particles, available from Saiden Chemical Industry Co., Ltd.), PRIMAL AC-22 and AC-61 (acrylic-based resin particles, available from Rohm & Haas Company), NANOCRYL SBCX-2821 and 3689 (acrylic- silicone-based resin particles, available from Toyo Ink Co., Ltd.), and #3070 (methyl methacrylate polymer resin particles, available from Mikuni Color Ltd.). One of these commercially available products may be used alone or two or more of these commercially available products may be used in combination. [0030]

<<Other components>>

The white ink may contain other components such as a defoaming agent, a preservative and a fungicide, and a corrosion inhibitor as needed.

[0031]

-Defoaming agent-

The defoaming agent has no particular limit. For example, silicone-based defoaming agents, polyether-based defoaming agents, and aliphatic acid ester-based defoaming agents are suitable. These can be used alone or in combination. Of these, silicone-based defoaming agents are preferable to easily break foams.

[0032]

-Preservatives and fungicides-

The preservatives and fungicides are not particularly limited. A specific example is 1,2- benzisothiazolin -3-on.

[0033]

-Corrosion inhibitor-

The corrosion inhibitor has no particular limit. Examples thereof are acid sulfite and sodium thiosulfate.

[0034]

The property of the white ink is not particularly limited and can be suitably selected to suit to a particular application. For example, viscosity, pH, etc. are preferably in the following ranges.

The viscosity of the white ink at 25 degrees C is preferably from 5 to 30 mPa· s and more preferably from 5 to 25 mPa· s to improve print density and text quality and obtain good dischargeability. The viscosity can be measured by, for example, a rotatory viscometer (RE SOL, manufactured by TOKI SANGYO CO., LTD.). The measuring conditions are as follows:

-Standard cone rotor (1°34’ x R24)

-Sample liquid amount: 1.2 mL

-Number of rotations: 50 rotations per minute (rpm)

-25 degrees C

-Measuring time: three minutes

The pH of the white ink is preferably from 7 to 12 and more preferably from 8 to 11 in terms of prevention of corrosion of metal materials contacting the white ink.

[0035]

The surface tension of the white ink is not particularly limited. When printing a pattern with a non- white ink and subsequently printing the white ink in a manner to be overlaid on the non white ink, the white ink to be printed afterwards may bleed or have cissing on the previously printed non-white ink depending on the surface tension of the non-white ink. [0036]

<Non- white ink>

The non-white ink contains water, a coloring material, an organic solvent, and a surfactant, and further contains other components as needed.

[0037]

<<Surfactant>>

It is preferable that the non- white ink contain an acetylene glycol surfactant as a surfactant. The acetylene glycol surfactant is not particularly limited and may be appropriately selected depending on the intended purpose. Examples of the acetylene glycol surfactant include, but are not limited to, SURFYNOL DF110D, SURFYNOL 104E, SURFYNOL 82, SURFYNOL 420, SURFYNOL 440, SURFYNOL 465, SURFYNOL 485, SURFYNOL PSA-336, SURFYNOL E1004, and SURFYNOL EXP4200 (all available from Nissin Chemical Co., Ltd.).

[0038]

In the present disclosure, the non- white ink contains an acetylene glycol surfactant, and the white ink contains a silicone surfactant. This improves wettability on the non-white ink to be printed previously and makes it possible to obtain a clear ink with little cissing.

[0039]

The non- white ink may contain any other surfactant in combination with the acetylene glycol surfactant.

Examples of the any other surfactant include, but are not limited to, silicone -based surfactants, fluorosurfactants, amphoteric surfactants, nonionic surfactants, anionic surfactants, etc.

The silicone-based surfactant has no specific limit and can be suitably selected to suit to a particular application. Of these, preferred are silicone-based surfactants which are not decomposed even in a high pH environment. Specific examples thereof include, but are not limited to, side-chain-modified polydimethylsiloxane, both end-modified polydimethylsiloxane, one-end-modified polydimethylsiloxane, and side-chain-both-end- modified polydimethylsiloxane. A silicone-based surfactant having a polyoxyethylene group or a polyoxyethylene polyoxypropylene group as a modifying group is particularly preferable because such an agent demonstrates good characteristics as an aqueous surfactant. It is possible to use a polyether-modified silicone-based surfactant as the silicone-based surfactant. A specific example thereof is a compound in which a polyalkylene oxide structure is introduced into the side chain of the Si site of dimethyl siloxane.

[0040]

Specific examples of the fluoro surfactants include, but are not limited to, perfluoroalkyl sulfonic acid compounds, perfluoroalkyl carboxylic acid compounds, perfluoroalkyl phosphoric acid ester compounds, adducts of perfluoroalkyl ethylene oxide, and polyoxyalkylene ether polymer compounds having a perfluoroalkyl ether group in its side chain. These are particularly preferable because they do not foam easily. Specific examples of the perfluoroalkyl sulfonic acid compounds include, but are not limited to, perfluoroalkyl sulfonic acid and salts of perfluoroalkyl sulfonic acid. Specific examples of the perfluoroalkyl carboxylic acid compounds include, but are not limited to, perfluoroalkyl carboxylic acid and salts of perfluoroalkyl carboxylic acid. Specific examples of the polyoxyalkylene ether polymer compounds having a perfluoroalkyl ether group in its side chain include, but are not limited to, sulfuric acid ester salts of polyoxyalkylene ether polymer having a perfluoroalkyl ether group in its side chain and salts of polyoxyalkylene ether polymers having a perfluoroalkyl ether group in its side chain. Counter ions of salts in these fluorine-based surfactants are, for example, Li, Na, K, NFL, NH₃CH₂CH₂OH,

Specific examples of the amphoteric surfactants include, but are not limited to, lauryl aminopropionic acid salts, lauryl dimethyl betaine, stearyl dimethyl betaine, and lauryl dihydroxy ethyl betaine.

Specific examples of the anionic surfactants include, but are not limited to, polyoxyethylene alkyl ether acetates, dodecyl benzene sulfonates, laurates, and polyoxyethylene alkyl ether sulfates.

These any other surfactants can be used alone or in combination.

[0042]

-Coloring material-

The coloring material has no particular limit. For example, pigments and dyes are suitable. The pigment includes inorganic pigments and organic pigments. These can be used alone or in combination. In addition, it is possible to use a mixed crystal.

As the pigments, for example, black pigments, yellow pigments, magenta pigments, cyan pigments, green pigments, orange pigments, gloss pigments of gold, silver, etc., and metallic pigments can be used.

As the inorganic pigments, in addition to barium yellow, cadmium red, and chrome yellow, carbon black manufactured by known methods such as contact methods, furnace methods, and thermal methods can be used.

As the organic pigments, it is possible to use azo pigments, polycyclic pigments (phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, indigo pigments, thioindigo pigments, isoindolinone pigments, and quinophthalone pigments, etc.), dye chelates (basic dye type chelates, acid dye type chelates, etc.), nitro pigments, nitroso pigments, and aniline black. Of these pigments, pigments having good affinity with solvents are preferable. Specific examples of the pigments for black include, but are not limited to, carbon black (C.I. Pigment Black 7) such as furnace black, lamp black, acetylene black, and channel black, metals such as copper, iron (C.I. Pigment Black 11), and titanium oxide, and organic pigments such as aniline black (C.I. Pigment Black 1).

[0043]

Specific examples of the pigments for color include, but are not limited to, C .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, 108, 109, 110, 117, 120, 138, 150, 153, 155, 180, 185, and 213; C.I. Pigment Orange 5, 13, 16, 17, 36, 43, and 51; C.I. Pigment Red 1, 2, 3, 5, 17, 22, 23, 31, 38, 48:2, 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 (rouge), 104, 105, 106, 108 (Cadmium Red), 112, 114, 122 (Quinacridone Magenta), 123, 146, 149, 166, 168, 170, 172, 177, 178, 179, 184, 185,

190, 193, 202, 207, 208, 209, 213, 219, 224, 254, and 264; C.I. Pigment Violet 1 (Rhodamine Lake), 3, 5:1, 16, 19, 23, and 38; C.I. PigmentBlue 1, 2, 15 (Phthalocyanine Blue), 15:1,

15:2, 15:3, 15:4 (Phthalocyanine Blue), 16, 17:1, 56, 60, and 63; and C.I. Pigment Green 1, 4, 7, 8, 10, 17, 18, and 36.

[0044]

The type of dye is not particularly limited and includes, for example, acidic dyes, direct dyes, reactive dyes, and basic dyes. These can be used alone or in combination.

Specific examples of the dye include, but are not limited to, C.I. Acid Yellow 17, 23, 42, 44, 79, and 142, C.I. Acid Red 52, 80, 82, 249, 254, and 289, C.I. Acid Blue 9, 45, and 249, C.I. Acid Black 1, 2, 24, and 94, C. I. Food Black 1 and 2, C.I. Direct Yellow 1, 12, 24, 33, 50, 55, 58, 86, 132, 142, 144, and 173, C.I. Direct Red 1, 4, 9, 80, 81, 225, and 227, C.I. Direct Blue 1, 2, 15, 71, 86, 87, 98, 165, 199, and 202, C.I. Direct Black 19, 38, 51, 71, 154, 168, 171, and 195, C.I. Reactive Red 14, 32, 55, 79, and 249, and C.I. Reactive Black 3, 4, and 35.

[0045]

The proportion of the coloring material in the non-white ink is preferably from 0.1 to 15 percent by mass and more preferably from 1 to 10 percent by mass in terms of enhancement of image density, fixability, and discharging stability.

[0046]

As the water, the organic solvent, the resin, and the other components of the non-white ink, the same water, organic solvent, resin, and other components as used in the white ink may be used.

[0047]

The property of the non- white ink is not particularly limited and can be suitably selected to suit to a particular application. For example, viscosity, surface tension, pH, etc., are preferably in the following ranges.

The viscosity of the ink at 25 degrees C is preferably from 5 to 30 mPa· s and more preferably from 5 to 25 mPa- s to improve print density and text quality and obtain good dischargeability. The viscosity can be measured by, for example, a rotatory viscometer (RE-80L, manufactured by TOKI SANGYO CO., LTD.). The measuring conditions are as follows:

-Standard cone rotor (1°34’ x R24)

-Sample liquid amount: 1.2 mL

-Number of rotations: 50 rotations per minute (rpm)

-25 degrees C

-Measuring time: three minutes [0048]

In order to enable the white ink to be leveled suitably and to suppress color bleed or cissing due to wetting and spreading conditions of the white ink even when there is no drying step between printing of the non-white ink to be printed previously and printing of the white ink to be printed subsequently, the surface tension of the non-white ink to be printed previously is preferably 20 mN/m or higher but 45 mN/m or lower, more preferably 30 mN/m or higher but 40 mN/m or lower, and still more preferably 35 mN/m or higher but 40 mN/m or lower, at 25 degrees C.

[0049]

The dynamic surface tension of the non-white ink according to the maximum bubble pressure technique at a surface lifetime of 15 msec is preferably 28 mN/m or higher but 43 mN/m or lower.

The pH of the non-white ink is preferably from 7 to 12 and more preferably from 8 to 11 in terms of prevention of corrosion of metal materials contacting the non-white ink.

[0050]

The processing fluid contains water, a flocculant, an organic solvent, and a surfactant, and further contains other components as needed.

[0051]

<<Flocculant>>

The flocculant is not particularly limited and may be appropriately selected depending on the intended purpose. Examples of the flocculant include, but are not limited to, water-soluble cation polymers, acids, and multivalent metal salts. Among these flocculants, multivalent metal salts are preferable.

[0052]

-Multivalent metal salt-

A multivalent metal salt flocculates the pigment contained in the ink quickly after a droplet of the ink lands, and suppresses color bleed and improves color developability.

A multivalent metal is not particularly limited and may be appropriately selected depending on the intended purpose. Examples of the multivalent metal include, but are not limited to, titanium compounds, chromium compounds, copper compounds, cobalt compounds, strontium compounds, barium compounds, iron compounds, aluminum compounds, calcium compounds, and magnesium compounds. Among these multivalent compounds, one or more selected from the group consisting of calcium compounds, magnesium compounds, nickel compounds, and aluminum compounds are preferable because of the ability to effectively flocculate the pigment contained in the ink, and divalent metal salts of, for example, calcium compounds and magnesium compounds are more preferable.

When the processing fluid contains a divalent metal salt as the flocculant, the processing fluid is stable without, for example precipitation of the flocculant, and is suitable for preventing bleed between the non-white ink and the white ink through promotion of a quick aggregation reaction between the inks.

[0053]

Examples of the divalent metal salt include, but are not limited to, calcium carbonate, calcium nitrate, calcium chloride, calcium acetate, calcium sulfate, magnesium chloride, magnesium acetate, magnesium sulfate, barium sulfate, zinc sulfide, and zinc carbonate.

[0054]

The content of the flocculant is preferably 4% by mass or greater and more preferably 6% by mass or greater relative to the total amount of the processing fluid. When the content of the flocculant is 4% by mass or greater, the processing fluid has an improved reactivity with the inks and can prevent bleed. The upper limit of the content of the flocculant is preferably 9% by mass or less in terms of storage stability.

[0055]

As the water, the organic solvent, the surfactant, and the other components contained in the processing fluid, the same water, organic solvent, surfactant, and other components as used in the white ink and the non-white ink may be used.

[0056]

Anon-permeating print medium, which is the print medium used in the present disclosure, has a surface with low moisture permeability and absorbency and includes a material having myriad of hollow spaces inside but not open to the outside. To be more quantitative, the non permeating print medium has a water-absorption amount of 10 mL/m² or less between the contact and 30 msec^1/2 after the contact according to Bristow method.

For example, vinyl chloride resin films, polyethylene terephthalate (PET) films, polypropylene, polyethylene, and polycarbonate films, and nylon films are suitably used for the non-permeating print medium.

[0057]

Examples of the polypropylene films include, but are not limited to, P-2002, P-2161, and P- 4166 available from Toyobo Co., Ltd., PA-20, PA-30, and PA-20W available from SUNTOX Co., Ltd., and FOA, FOS, and FOR available from Futamua Chemical Co., Ltd.

Examples of the polyethylene terephthalate films include, but are not limited to, E-5100 and E-5102 available from Toyobo Co., Ltd., P60 and P375 available from Toray Industries, Inc., and G2, G2P2, K, and SL available from Teijin DuPont Film Co., Ltd. Examples of the nylon films include, but are not limited to, HARDEN FILM N-l 100, N- 1102, and N-1200 available from Toyobo Co., Ltd., and ON, NX, MS, and NK available from Unitika Ltd.

[0058]

(Image forming method and image forming apparatus)

An image forming method of the present disclosure includes a processing fluid applying step of applying the processing fluid included in the set of a processing fluid and inks of the present disclosure to a non-permeating print medium, a non- white ink applying step of applying the non- white ink included in the set of a processing fluid and inks of the present disclosure, and a white ink applying step of applying the white ink included in the set of a processing fluid and inks of the present disclosure, and further includes other steps as needed. [0059]

An image forming apparatus of the present disclosure includes a processing fluid storing unit configured to store the processing fluid included in the set of a processing fluid and inks of the present disclosure, an ink storing unit configured to store the white ink and the non-white ink included in the set of a processing fluid and inks of the present disclosure, a processing fluid applying unit configured to apply the processing fluid to a non-permeating print medium, a non-white ink applying unit configured to apply the non-white ink, and a white ink applying unit configured to apply the white ink, and further includes other units as needed.

The lower limit of the total amount of application of the non-white ink and the white ink is not particularly limited. On the other hand, the upper limit of the total amount of application of the non-white ink and the white ink is preferably 40 micrograms/inch² or less, more preferably 20 micrograms/inch² or less, and yet more preferably 10 micrograms/inch² or less because it is preferable that the amount of the inks be lower in order to suppress bleed. According to an image forming method by which the total amount of application of the non white ink and the white ink is 20 micrograms/inch² or less, the inks on the base material entirely react with the processing fluid without exception and aggregate, so the inks quickly lose fluidity and tend not to bleed. The abundance of the flocculant is preferably 0.09 milligrams/inch² or greater.

The breakdown of the amounts of application of the non-white ink and the white ink is not particularly limited. The number of inks to be used may also be arbitrary. For example, one non- white ink may be used alone or two or more non- white inks may be used in combination. [0060]

According to an image forming method including a non-white ink drying step of drying the non- white ink between the non- white ink applying step and the white ink applying step, it is possible to apply a new ink on an ink that has been applied previously and dried and has lost fluidity. This eliminates mixing of the inks on the non-permeating print medium, and can provide a clear image with little bleed.

The drying unit is not particularly limited and may be appropriately selected depending on the intended purpose so long as the drying unit can dry the printed surface and the back surface of a print medium. Examples of the drying unit include, but are not limited to, a hot air heater, an infrared heater, a heating roller, and a hot plate.

[0061]

It is preferable that the image forming method include a surface reforming step of reforming a surface of a non-permeating print medium. It is preferable to perform the surface reforming step before applying the inks included in the set of a processing fluid and inks to the non permeating print medium.

It is preferable to reform a surface of a non-permeating print medium, because wettability of the inks on the non-permeating print medium is improved and an image having no cissing can be obtained.

Examples of the surface treatment include, but are not limited to, corona treatment, atmospheric plasma treatment, flame treatment, and ultraviolet irradiation treatment. Among these surface treatments, a corona treatment step of applying corona treatment to a print surface is preferable as the surface reformation for the print surface. It is preferable to employ corona treatment because of excellent stability of corona discharge output and uniformity of surface treatment on the print surface compared with atmospheric plasma treatment, flame treatment, and ultraviolet irradiation treatment.

[0062]

The set of inks and a processing fluid of the present disclosure can be suitably applied to various printing apparatuses employing an inkjet printing method such as printers, facsimile machines, photocopiers, multifunction peripherals (serving as a printer, a facsimile machine, and a photocopier), and 3D model manufacturing devices (3D printers, additive manufacturing device).

In the present disclosure, the image forming apparatus and the image forming method represent an apparatus capable of discharging ink, various processing fluids, etc. to a print medium and a method printing an image on the print medium using the apparatus. The print medium means an article to which the ink or the various processing fluids can be attached at least temporarily. Furthermore, in addition to the desktop type, this printing apparatus includes a wide type capable of printing images on a large print medium such as A0, a continuous printer capable of using continuous paper wound up in a roll form as print media. FIG. 1 illustrates an example of the image forming apparatus.

The steps of applying inks and the step of applying a pre-processing fluid included in the image forming method of the present disclosure may be performed by the same printing apparatus or may be performed by different printing apparatuses.

[0063]

The image forming apparatus 100 of FIG. 1 includes a pre-processing fluid applying unit 110, an ink applying unit 120, a post-processing fluid applying unit 130, a drying unit 140, and a conveying unit 150. The pre-processing fluid applying unit 110 is configured to apply a pre processing fluid to a print medium M. The pre-processing fluid applying unit 110, the post-processing fluid applying unit 130, the drying unit 140, and the conveying unit 150 may be omitted.

[0064]

The method for applying the pre-processing fluid is not particularly limited. Examples of the method include, but are not limited to, an inkjet method, a roller coating method, a blade coating method, a gravure coating method, a gravure offset coating method, a bar coating method, a roll coating method, a knife coating method, an air knife coating method, a comma coating method, a U comma coating method, an AKKU coating method, a smoothing coating method, a microgravure coating method, a reverse roll coating method, a four- or five-roll coating method, a dip coating method, a curtain coating method, a slide coating method, and a die coating method.

The pre-processing fluid applying unit 110 may be omitted because images mage be printed by the image forming apparatus after the pre-processing fluid is previously applied on a print medium manually by, for example, a bar coating method.

[0065]

The print medium M used for printing is not particularly limited. Examples of the print medium M include, but are not limited to, plain paper, gloss paper, special paper, cardboard, cloths, films, OHP sheets, and general-purpose print paper.

[0066]

The ink applying unit 120 is configured to apply an inkjet ink on a surface of the print medium M on which the pre-processing fluid is applied.

For example, a known inkjet head may be used as the ink applying unit 120.

The ink applying unit 120 may be a head configured to discharge an ink having an arbitrary color, and may include heads configured to discharge inks of, for example, Y (yellow), M (magenta), C (cyan), K (black), and W (white) as needed.

[0067]

The post-processing fluid applying unit 130 needs at least to be able to apply a post processing fluid to a region to which an inkjet ink has been applied on a surface of the print medium M to which the inkjet ink has been applied. In addition to an inkjet head, for example, spray or a roller may be used as the post-processing fluid applying unit.

The post-processing fluid applying nit 130 may be omitted.

[0068]

The method for applying the post-processing fluid is not particularly limited. Examples of the method include, but are not limited to, an inkjet method, a roller coating method, a blade coating method, a gravure coating method, a gravure offset coating method, a bar coating method, a roll coating method, a knife coating method, an air knife coating method, a comma coating method, a U comma coating method, an AKKU coating method, a smoothing coating method, a microgravure coating method, a reverse roll coating method, a four- or five-roll coating method, a dip coating method, a curtain coating method, a slide coating method, and a die coating method. [0069]

The drying unit 140 is configured to dry the print medium M to which the post-processing fluid is applied with hot air. When there is no post-processing fluid applying unit, the drying unit 140 may be omitted.

The drying unit 140 may dry the print medium M to which the post-processing fluid is applied by heating using, for example, infrared rays, microwaves, or a roll heater instead of hot air, or the print medium M to which the post-processing fluid is applied may be dried naturally without actuation of the drying unit 140.

[0070]

The conveying unit 150 is configured to convey the print medium M.

The conveying unit 150 is not particularly limited so long as the conveying unit 150 can convey the print medium M. Examples of the conveying unit 150 include, but are not limited to, a conveyor belt and a platen.

[0071]

The image forming apparatus 100 may further include a fixing unit configured to heat and fix the image formed on the print medium M. The fixing unit is not particularly limited. Examples of the fixing unit include, but are not limited to, a fixing roller.

[0072]

When using a desktop printer as the image forming apparatus, as an example of the pre processing fluid applying unit and the post-processing fluid applying unit, as in the case of the ink such as black (K), cyan (C), magenta (M), yellow (Y), and white (W), a liquid container containing a pre-processing fluid or a post-processing fluid and a liquid discharging head are added to discharge the pre-processing fluid or the post-processing fluid in an inkjet printing method.

[0073]

Moreover, image forming, recording, printing, etc. in the present disclosure represent the same meaning.

Print media, media, and print targets represent the same meaning.

[Examples]

[0074]

The present disclosure will be described below by way of Examples. The present disclosure should not be construed as being limited to these Examples.

[0075]

(Pigment dispersion liquid preparation example 1)

Preparation of black pigment dispersion liquid >

After the mixture of the components of the prescription described below was pre-mixed, the resultant was subjected to circulation dispersion treatment for 7 hours using a disk-type bead mill (obtained from Shinmaru Enterprises Corporation, KDL type, using zirconia balls having a diameter of 0.3 mm as media), to obtain a black pigment dispersion liquid (with a pigment concentration of 15% by mass). <Prescription of black pigment dispersion liquid >

-Carbon black pigment (product name: MONARCH 800, obtained from Cabot Corporation): 15 parts by mass

-Acrylic-based polymeric dispersant (product name: DISPERBYK-2010, obtained from BYK Japan KK): 5 parts by mass -Ion-exchanged water: 80 parts by mass [0076]

(Pigment dispersion liquid preparation example 2)

Preparation of cyan pigment dispersion liquid>

A cyan pigment dispersion liquid (with a pigment solid concentration of 15 % by mass) was obtained in the same manner as in Pigment dispersion liquid preparation example 1, except that the carbon black pigment of Pigment dispersion liquid preparation example 1 was changed to Pigment Blue 15:3.

[0077]

(Pigment dispersion liquid preparation example 3)

Preparation of magenta pigment dispersion liquid>

A magenta pigment dispersion liquid (with a pigment solid concentration of 15% by mass) was obtained in the same manner as in Pigment dispersion liquid preparation example 1, except that the carbon black pigment of Pigment dispersion liquid preparation example 1 was changed to Pigment Red 269.

[0078]

(Pigment dispersion liquid preparation example 4)

Preparation of yellow pigment dispersion liquid>

A yellow pigment dispersion liquid (with a pigment solid concentration of 15% by mass) was obtained in the same manner as in Pigment dispersion liquid preparation example 1, except that the carbon black pigment of Pigment dispersion liquid preparation example 1 was changed to Pigment Yellow 74.

[0079]

(Pigment dispersion liquid preparation example 5)

Preparation of white pigment dispersion liquid 1 >

Titanium oxide (product name: STR-100W, obtained from Sakai Chemical Industry Co., Ltd.) (25 parts by mass), a pigment dispersant (product name: TEGO DISPERS 651, obtained from Evonik Industries AG) (5 parts by mass), and water (70 parts by mass) were mixed, and subjected to dispersion treatment for 5 minutes at 8 m/s with a bead mill (product name: RESEARCH LAB, obtained from Shinmaru Enterprises Corporation) using zirconia beads having a diameter of 0.3 mm at a packing ratio of 60%, to obtain a white pigment dispersion liquid 1 (with a pigment solid concentration of 25% by mass).

[0080]

(Pigment dispersion liquid preparation example 6)

Preparation of white pigment dispersion liquid 2> A white pigment dispersion liquid 2 (with a pigment solid concentration of 25% by mass) was obtained in the same manner as in Pigment dispersion liquid preparation example 5, except that unlike in Pigment dispersion liquid preparation example 5, the amount of the pigment dispersant was changed to 7 parts by mass and the amount of water was changed to 68 parts by mass.

[0081]

(Pigment dispersion liquid preparation example 7)

Preparation of white pigment dispersion liquid 3>

A white pigment dispersion liquid 3 (with a pigment solid concentration of 25% by mass) was obtained in the same manner as in Pigment dispersion liquid preparation example 5, except that unlike in Pigment dispersion liquid preparation example 5, the amount of the pigment dispersant was changed to 3 parts by mass and the amount of water was changed to 72 parts by mass.

[0082]

(Pigment dispersion liquid preparation example 8)

Preparation of white pigment dispersion liquid 4>

A white pigment dispersion liquid 4 (with a pigment solid concentration of 25% by mass) was obtained in the same manner as in Pigment dispersion liquid preparation example 5, except that unlike in Pigment dispersion liquid preparation example 5, the amount of the pigment dispersant was changed to 9 parts by mass and the amount of water was changed to 66 parts by mass.

[0083]

(Pigment dispersion liquid preparation example 9)

Preparation of white pigment dispersion liquid 5>

A white pigment dispersion liquid 5 (with a pigment solid concentration of 25% by mass) was obtained in the same manner as in Pigment dispersion liquid preparation example 5, except that unlike in Pigment dispersion liquid preparation example 5, the amount of the pigment dispersant was changed to 11 parts by mass and the amount of water was changed to 64 parts by mass.

[0084]

(Resin dispersion liquid production example 1)

-Production of resin dispersion liquid 1-

A mixture containing methyl methacrylate (65 parts by mass), 2-ethylhexyl acrylate (31 parts by mass), methacrylic acid (2 parts by mass), AQUALON HS-10 (obtained from DKS Co., Ltd.) (2 parts by mass), and ion-exchanged water (52 parts by mass) was emulsified using a homomixer, to obtain a homogenous opalescent emulsified liquid.

Ion-exchanged water (89 parts by mass) was added into a 250 mL flask equipped with a stirrer, a thermometer, a nitrogen gas introducing pipe, and a reflux condenser, and subjected to temperature elevation to 70 degrees C while nitrogen was being introduced. Next, a 10% by mass aqueous solution (0.8 parts by mass) of AQUALON HS-10 (obtained from DKS Co., Ltd.) and a 5% by mass ammonium persulfate aqueous solution (2.6 parts by mass) were added to the resultant, and the emulsified liquid prepared previously was subsequently dropped continuously into the resultant for 2.5 hours. Until when three hours passed since dropping was started, a 5% by mass ammonium persulfate aqueous solution (0.6 parts by mass) was added to the resultant once every hour. After dropping was completed, the resultant was aged at 70 degrees C for 2 hours, subsequently cooled, and adjusted to pH of from 7 through 8 with 28% by mass ammonia water, to obtain a resin dispersion liquid 1.

The glass transition temperature (Tg) of the obtained resin was 53 degrees C. The glass transition temperature (Tg) was measured by differential scanning calorimetry (DSC) (obtained from Rigaku Corporation, THERMO PLUS EV02/DSC).

[0085]

(Resin dispersion liquid production example 2)

-Production of resin dispersion liquid 2-

A resin dispersion liquid 2 was obtained in the same manner as in Resin dispersion liquid production example 1, except that unlike in Resin dispersion liquid production example 1, the amount of methyl methacrylate was changed to 69 parts by mass and the amount of 2- ethylhexyl acrylate was changed to 27 parts by mass. The glass transition temperature (Tg) of the obtained resin measured in the same manner as in Resin dispersion liquid production example 1 was 62 degrees C.

[0086]

(Resin dispersion liquid production example 3)

-Production of resin dispersion liquid 3-

A resin dispersion liquid 3 was obtained in the same manner as in Resin dispersion liquid production example 1, except that unlike in Resin dispersion liquid production example 1, the amount of methyl methacrylate was changed to 77 parts by mass and the amount of 2- ethylhexyl acrylate was changed to 19 parts by mass. The glass transition temperature (Tg) of the obtained resin measured in the same manner as in Resin dispersion liquid production example 1 was 85 degrees C.

[0087]

(Resin dispersion liquid production example 4)

Preparation of urethane resin emulsion A>

Dicyclohexylmethane diisocyanate (1.4 moles) relative to 1,6-hexanediol (1 mole), a diisocyanate compound (0.1 moles) obtained by allowing polyethylene glycol monomethyl ether having a molecular weight of 1,000 (1/3 moles) to undergo a reaction with 1,6- hexamethylene diisocyanate isocyanurate trimer (1 mole), and N-methyl-2-pyrrolidone (15% by mass of the whole mass) were added into a reaction flask, and allowed to undergo a reaction under a nitrogen stream at 90 degrees C for 2 hours, to obtain a prepolymer.

The above-obtained prepolymer (450 g) having a solid concentration of 85% by mass was dropped for 15 minutes into water (600 g) in which a silicone-based defoaming agent (SE-21, obtained from Wacker Silicone Co., Ltd.) (0.2 g) was dissolved, and the resultant was stirred at 25 degrees C for 10 minutes. Subsequently, a compound represented by Structural formula (A) below, ethylene diamine, and adipic acid hydrazide were dropped into the resultant, to obtain a polyurethane resin emulsion A.

[0088]

[Chem. 1]

HiN-CaHe-Si-f-OCzHs^

—Structural formula (A)

[0089]

(Non-white ink preparation example 1)

-Preparation of non-white ink 1 -

The components of the non-white ink prescription described below were mixed and stirred, and filtrated through a polypropylene filter having an average pore diameter of 0.8 micrometers, to produce a non -white ink 1.

<Non- white ink prescription>

-Black pigment dispersion liquid: 20 parts by mass

-SURFYNOL 420 (obtained from Nissin Chemical Co., Ltd.): 0.5 parts by mass

-1, 2-Propanediol: 15 parts by mass

-Ethylene glycol monobutyl ether: 10 parts by mass

-PROXEL LV (obtained from Avecia Inc., preservative): 0.1 parts by mass -Resin dispersion liquid 1 described above: 10 parts by mass -Ion-exchanged water: balance (total: 100 parts by mass)

[0090]

(Non-white ink preparation examples 2 to 6)

-Preparation of non-white inks 2 to 6-

Non-white inks 2 to 6 were prepared in the same manner as in Non-white ink preparation example 1, except that the non-white ink prescription of Non-white ink preparation example 1 was changed as described in Table 1. The values of the resin dispersion liquids in Table 1 represent the resin contents converted to solid concentrations.

[0091]

Next, the static surface tension of the obtained non-white inks was measured in the manner described below. The results are presented in Table 1.

[0092]

The static surface tension of the non-white inks was measured with an automatic surface tensiometer (DY-300, obtained from Kyowa Interface Science Co., Ltd) at 25 degrees C.

More specifically, the non-white ink was poured into a petri dish having a diameter of 30 mm, left to stand still for 5 minutes, and measured with the automatic surface tensiometer DY-300 by Wilhelmy method using a platinum plate.

[0093] [Table 1]

[0094]

The details of the components in Table 1 are as follows.

-Surfactant-

-SURFYNOL 420 (acethylene glycol surfactant, obtained from Nissin Chemical Co., Ltd.) -SURFYNOL PSA-336 (acethylene glycol surfactant, obtained from Nissin Chemical Co., Ltd.)

-SURFYNOL 440 (acethylene glycol surfactant, obtained from Nissin Chemical Co., Ltd.) -SURFYNOL 465 (acetylene glycol surfactant, obtained from Nissin Chemical Co., Ltd.) -BYK-333 (silicone surfactant, obtained from BYK Chemie Japan Co., Ltd.)

-FS-300 (fluorosurfactant, obtained from DuPont)

[0095]

(White ink preparation example 1)

-Preparation of white ink 1-

The components of the white ink prescription described below were mixed and stirred, and filtrated through a polypropylene filter having an average pore diameter of 0.8 micrometers, to produce a white ink 1.

-White pigment dispersion liquid 2: 48 parts by mass

-BYK-333 (silicone surfactant, obtained from BYK Chemie Japan Co., Ltd.): 0.5 parts by mass -1, 2-Propanediol: 15 parts by mass -Ethylene glycol monobutyl ether: 10 parts by mass -ROXEL LV (Avecia Inc., preservative): 0.1 parts by mass -Resin dispersion liquid 1 described above: 10 parts by mass -Ion-exchanged water: balance (total: 100 parts by mass)

[0096]

(White ink preparation examples 2 to 11)

-Preparation of white inks 2 to 11-

White inks 2 to 11 were produced in the same manner as in White ink preparation example 1, except that the white ink prescription of White ink preparation example 1 was changed as described in Table 2-1 and Table 2-2. The values of the resin dispersion liquids in Table 2-1 and Table 2-2 represent the resin contents converted to solid concentrations.

[0097]

Next, the rate of initial increase of the particle diameter of the obtained white inks was measured in the manner described below. The results are presented in Table 2-1 and Table 2-

2

[0098]

A 1% by mass calcium acetate aqueous solution (0.5 mL) was mixed in a 1% by volume white ink aqueous solution (4 mL), and the rate of initial increase of the particle diameter was measured from the start of mixing until after 20 seconds. The particle diameter was measured using a particle diameter measuring system (obtained from Otsuka Electronics Co., Ltd., ELSZ-1000S) according to a cumulant method. The 1% by volume white ink aqueous solution and the 1% by mass calcium acetate aqueous solution were mixed with each other, the particle diameter of the resultant was measured by a cumulant method at intervals of some seconds from the start of mixing, the particle diameter data were plotted to draw a straight line, and the rate of initial increase of the particle diameter (nm/second) was calculated based on the slope of the linear approximation from the start of mixing (0 seconds) until after 20 seconds.

[0099] [Table 2-1]

[0100] [Table 2-2]

[0101]

The details of the components in Table 2-1 and Table 2-2 are as follows.

-Surfactant-

-BYK-333 (silicone surfactant, obtained from BYK Chemie Japan Co., Ltd.)

-BYK-3450 (silicone surfactant, obtained from BYK Chemie Japan Co., Ltd.)

-WET-260 (silicone surfactant, obtained from Evonik Industries AG)

-WET-270 (silicone surfactant, obtained from Evonik Industries AG)

-WET-280 (silicone surfactant, obtained from Evonik Industries AG)

-SAG503A (silicone surfactant, obtained from Nissin Chemical Co., Ltd.)

-FS-300 (fluorosurfactant, obtained from DuPont)

-SURFYNOL 420 (acetylene glycol surfactant, obtained from Nissin Chemical Co., Ltd.)

[0102]

(Processing fluid preparation example 1)

-Preparation of processing fluid 1-

The components of the processing fluid 1 were prepared at the mix proportions described below, and then mixed and stirred, and filtrated through a filter having an average pore diameter of 5 micrometers (obtained from Sartorius AG, MINISART). <Processing fluid prescription

-1,2-Propanediol: 15 parts by mass

-Ethylene glycol monobutyl ether: 13 parts by mass

-EMULGEN LS-106 (obtained from Kao Corporation, polyoxyalkyl ether surfactant): 0.5 parts by mass

-Magnesium sulfate: 6 parts by mass

-PROXEL LV (obtained from Avecia Inc., preservative): 0.1 parts by mass -Ion-exchanged water: balance (total: 100 parts by mass)

[0103]

(Processing fluid preparation examples 2 to 8)

-Preparation of processing fluids 2 to 8-

Processing fluids 2 to 8 were prepared in the same manner as in Processing fluid preparation example 1, except that the processing fluid prescription of Processing fluid preparation example 1 was changed as described in Table 3.

[0104]

[Table 3]

[0105]

The details of the components in Table 3 are as follows.

-Surfactant-

-EMULGEN LS-106 (polyoxyalkyl ether surfactant, obtained from Kao Corporation) -BYK-333 (silicone surfactant, obtained from BYK Chemie Japan Co., Ltd.) -BYK-3450 (silicone surfactant, obtained from BYK Chemie Japan Co., Ltd.) -WET-270 (silicone surfactant, obtained from Evonik Industries AG) -WET-280 (silicone surfactant, obtained from Evonik Industries AG)

-SAG503A (silicone surfactant, obtained from Nissin Chemical Co., Ltd.)

-SAG016 (silicone surfactant, obtained from Nissin Chemical Co., Ltd.)

[0106]

(Examples 1 to 21 and Comparative Examples 1 and 2)

For the white ink, the non-white ink, and the processing fluid of the combinations presented in Table 4-1 to Table 4-5, an image forming apparatus (IPSIO GXE-5500, obtained from Ricoh Company, Ltd.) was adjusted through changing of the drive voltage for a piezo element in a manner that the amounts of the white ink and the non-white ink to be discharged would be the same under environmental conditions adjusted to 23 degrees C + 0.5 degrees C and 50+5% RH.

The processing fluid was applied in a coating amount of 1.5 g/m² on OPP (obtained from Toyobo Co., Ltd, PYRENE P2102) using a bar coater No. 1, and subsequently dried at 80 degrees C for 2 minutes. According to a chart (see FIG. 2) including a solid image of a non white ink in a solid image of a white ink, the white ink and the non- white ink were printed on the dried OPP using an image forming apparatus. The total amount of application of the white ink and the non-white ink was as presented in Table 4-1 to Table 4-5.

OPP (obtained from Toyobo Co., Ltd., PYRENE P2102) was cut into an appropriate size and used. The white ink and the non-white ink were discharged in a manner that after the non white ink was discharged, the white ink was discharged to have a boundary against the non white ink. When there was an ink drying step between the non- white ink applying step and the white ink applying step, the drying step was performed at 80 degrees C for 2 minutes between the non-white ink applying step and the white ink applying step.

[0107]

Next, various properties were evaluated in the manners described below. The results are presented in Table 4-1 to Table 4-5.

[0108]

The solid image formed as described above was visually observed for the degree of bleed, and bleed evaluation was performed according to the criteria described below based on the condition of the solid image of the non- white ink that should have had been covered with the white ink. The ratings C, B, A— and A are in the tolerable range.

A: There was no bleed at all.

A — : There was bleed of a level indiscernible unless the portions where the non- white ink and the whit ink overlapped were watched closely.

B: There was an insignificant visually-observable bleed at the edges of the solid image of the non- white ink.

C: There was a slight visually-observable bleed at the edges of the solid image of the non white ink. D: There was a significant bleed at the edges of the solid image of the non-white ink.

E: The non-white ink and the white ink bled overall.

[0109]

The solid image formed as described above was visually observed for the degree of cissing, and cissing evaluation was performed according to the criteria described below based on the condition of the solid image of the non- white ink that should have had been covered with the white ink. The ratings C, B, and A are in the tolerable range.

A: The solid image of the non-white ink was not exposed, and the solid image of the white ink was uniform.

B: The solid image of the non- white ink was not exposed, but the solid image of the white ink was slightly nonuniform.

C: The solid image of the non- white ink was not exposed, but the solid image of the white ink was nonuniform.

D: The solid image of the non-white ink was exposed.

[0110]

A processing fluid was produced, and stored at room temperature (25 degrees C) for 1 week. The appearance of the processing fluid after storage was visually observed, to evaluate processing fluid stability according to the criteria described below. The ratings B and A are in the tolerable range.

A: There was nothing like precipitation of a metal salt even after 1 week, and the fluid was uniformly clear overall.

B: The fluid was uniformly clear overall immediately after the processing fluid was produced, but the fluid became cloudy or a metal salt precipitated after storage for 1 week.

C: The fluid was not uniform immediately after the processing fluid was produced, and cloudiness or a metal salt remaining undissolved were observed.

[0111] [Table 4-1]

[0112] [Table 4-2]

[0113] [Table 4-3] [0114] [Table 4-4]

[0115] [Table 4-5]

[0116]

Aspects of the present disclosure are, for example, as follows.

<1> A set of a processing fluid and inks, the set including: a processing fluid containing a flocculant; a non-white ink containing a coloring material other than a white color; and a white ink containing a white coloring material, wherein when a 1% by volume aqueous solution obtained by diluting the white ink with water and a 1% by mass calcium acetate aqueous solution are mixed with each other, a rate of initial increase of a particle diameter from start of mixing until after 20 seconds is 30 nm/second or greater.

<2> The set according to <1>, wherein the set is used for forming an image on a non-permeating print medium.

<3> The set according to <1> or <2>, wherein the flocculant is a divalent metal salt.

<4> The set according to any one of <1> to <3>, wherein a content of the flocculant is 6% by mass or greater relative to a total amount of the processing fluid.

<5> The set according to any one of <1> to <4>, wherein the non-white ink contains an acetylene glycol surfactant, and the white ink contains a silicone surfactant.

<6> An image forming method, including: applying the processing fluid included in the set according to any one of <1> to <5> to a non permeating print medium; applying the non- white ink included in the set according to any one of <1> to <5>; and applying the white ink included in the set according to any one of <1> to <5>.

<7> The image forming method according to <6>, wherein a total amount of application of the non- white ink and the white ink is 20 micrograms/inch² or less.

<8> The image forming method according to <6> or <7>, further including drying the non-white ink between the applying the non-white ink and the applying the white ink.

<9> An image forming apparatus, including: a processing fluid storing unit configured to store the processing fluid included in the set according to any one of <1> to <5>; an ink storing unit configured to store the non- white ink and the white ink included in the set according to any one of <1> to <5>; a processing fluid applying unit configured to apply the processing fluid to a non-permeating print medium; a non-white ink applying unit configured to apply the non- white ink; and a white ink applying unit configured to apply the white ink.

[0117]

The set of a processing fluid and inks according to any one of <1> to <5>, the image forming method according to any one of <6> to <8>, and the image forming apparatus according to <9> can solve the various problems in the related art and achieve the object of the present disclosure.

[0118]

The above-described embodiments are illustrative and do not limit the present invention. Thus, numerous additional modifications and variations are possible in light of the above teachings. For example, elements and/or features of different illustrative embodiments may be combined with each other and/or substituted for each other within the scope of the present invention.

[0119]

This patent application is based on and claims priority to Japanese Patent Application No. 2021-034304, filed March 4, 2021, Japanese Patent Application No. 2021-201678, filed December 13, 2021, and Japanese Patent Application No. 2021-212739, filed December 27, 2021, in the Japan Patent Office, the entire disclosure of each of which is hereby incorporated by reference herein.

[Reference Signs List]

[0120]

100: image forming apparatus

110: pre-processing fluid applying unit

120: ink applying unit

130: post-processing fluid applying unit

140: drying unit

150: conveying unit

M: print medium

Claims

[CLAIMS]

[Claim 1]

A set of a processing fluid and inks, the set comprising: a processing fluid containing a flocculant; a non-white ink containing a coloring material other than a white color; and a white ink containing a white coloring material, wherein when a 1% by volume aqueous solution obtained by diluting the white ink with water and a 1% by mass calcium acetate aqueous solution are mixed with each other, a rate of initial increase of a particle diameter from start of mixing until after 20 seconds is 30 nm/second or greater.

[Claim 2]

The set according to claim 1, wherein the set is used for forming an image on a non-permeating print medium.

[Claim 3]

The set according to claim 1 or 2, wherein the flocculant is a divalent metal salt.

[Claim 4]

The set according to any one of claims 1 to 3 , wherein a content of the flocculant is 6% by mass or greater relative to a total amount of the processing fluid.

[Claim 5]

The set according to any one of claims 1 to 4, wherein the non-white ink contains an acetylene glycol surfactant, and the white ink contains a silicone surfactant.

[Claim 6]

An image forming method, comprising: applying the processing fluid included in the set according to any one of claims 1 to 5 to a non-permeating print medium; applying the non- white ink included in the set according to any one of claims 1 to 5 ; and applying the white ink included in the set according to any one of claims 1 to 5.

[Claim 7]

The image forming method according to claim 6, wherein a total amount of application of the non- white ink and the white ink is 20 micrograms/inch² or less.

[Claim 8]

The image forming method according to claim 6 or 7, further comprising drying the non-white ink between the applying the non-white ink and the applying the white ink.

[Claim 9]

An image forming apparatus, comprising: a processing fluid storing unit configured to store the processing fluid included in the set according to any one of claims 1 to 5; an ink storing unit configured to store the non- white ink and the white ink included in the set according to any one of claims 1 to 5; a processing fluid applying unit configured to apply the processing fluid to a non-permeating print medium; a non-white ink applying unit configured to apply the non- white ink; and a white ink applying unit configured to apply the white ink.