Image formation method

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

[Technical Field]

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

[0002] The inkjet recording method has been rapidly gaining popularity in recent years because it allows for easy recording of color images, has low running costs, etc. However, this method has the problem that, depending on the combination of ink and recording medium, image defects such as character bleeding are likely to occur, resulting in a significant decrease in image quality. Therefore, a technique is known in which the recording medium is pretreated in advance using a pretreatment liquid containing a cationic compound or the like. Furthermore, when printing on a dark-colored recording medium, a technique is known in which a white base is formed by applying white ink to a recording medium to which a pretreatment liquid has been applied, and color inks are then applied to the white base to improve the color development of the image.

[0003] For example, Patent Document 1 discloses an inkjet textile printing method including the steps of applying a treatment liquid to at least an inkjet ink print area of a fabric, heating the fabric to which the treatment liquid has been applied, printing a white ink composition for inkjet textile printing in the inkjet ink print area to which the treatment liquid has been applied, and printing a colored ink composition for inkjet textile printing other than white. Summary of the Invention [Problem to be solved by the invention]

[0004] However, when white ink is applied to a recording medium and then color ink is applied to the area of the recording medium to which the white ink has been applied, there is a problem in that color bleeding occurs. [Means for solving the problem]

[0005] The present invention relates to an ink set having a white ink and color inks, wherein the difference in static surface tension between the white ink and the color inks at 25°C is 1.0 mN / m or less, and the differences in dynamic surface tension between the white ink and the color inks at 25°C when the bubble lifetimes, measured by the maximum bubble pressure method, are each independently 1.0 mN / m or less. [Effects of the Invention]

[0006] According to the present invention, it is possible to provide an ink set that suppresses the occurrence of color bleeding when a white ink is applied to a recording medium and then a color ink is applied to the area of the recording medium where the white ink has been applied. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic diagram showing an example of an image forming apparatus. [Figure 2] FIG. 2 is a schematic diagram showing an example of the containing means. [Figure 3] FIG. 3 is a schematic diagram showing a chart printed using an inkjet printing device. DETAILED DESCRIPTION OF THE INVENTION

[0008] An embodiment of the present invention will be described below.

[0009] <<Ink set>> The ink set of the present disclosure preferably includes a white ink and color inks, and optionally includes a pretreatment liquid, etc. The white ink and color ink may each be one or more. In the present disclosure, an "ink set" is sufficient as long as the white ink and the color inks are present in an independent state, and is not limited to, for example, a case in which a white ink containing means for containing the white ink and a color ink containing means for containing the color inks are manufactured, sold, etc. in an integrated state. For example, even if the white ink containing means and the color ink containing means are manufactured, sold, etc. independently, they are included in the ink set if they are based on the premise that the white ink and the color inks will be used in combination, or if they substantially lead to the white ink and the color inks being used in combination. The "white ink" in the present disclosure is a liquid composition that forms a white image by being applied to a recording medium. When a pretreatment liquid is used, the white ink is a liquid composition that forms a white image by being applied to an 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 color inks that are applied to the area to which the white ink has been applied, thereby improving the color development of the color image. Note that "white" refers to a color commonly referred to as white or white, and also includes colors that are lightly colored. In the present disclosure, a "color ink" is a liquid composition that forms a color image by being applied to an area of a recording medium to which a white ink has been applied. Note that the term "color" refers to colors not included in the above-mentioned "white," and includes, for example, black, cyan, magenta, and yellow. The "pretreatment liquid" in the present disclosure is a liquid composition that is applied to a recording medium and causes aggregation or thickening of the white ink or color ink upon contact with the white ink or color ink that is subsequently applied to the area where the pretreatment liquid has been applied.

[0010] The difference in static surface tension at 25°C between the white ink and color inks contained in the ink set is 1.0 mN / m or less, preferably 0.8 mN / m or less, more preferably 0.6 mN / m or less, and even more preferably 0.5 mN / m or less. The above difference in static surface tension is expressed as an absolute value and is 0 mN / m or more. When multiple white inks or color inks are used, it is sufficient that the above difference in static surface tension is satisfied for a given combination of white ink and color ink, but it is preferable that the above difference in static surface tension is satisfied for all combinations of white ink and color ink. Furthermore, the difference in dynamic surface tension between the white ink and the color inks at 25°C when the bubble lifetime is 15 msec, 150 msec, and 1500 msec as measured by the maximum bubble pressure method is independently 1.0 mN / m or less, and preferably 0.9 mN / m or less. The above-mentioned difference in dynamic surface tension is expressed as an absolute value and is 0 mN / m or more. When multiple white inks or color inks are used, it is sufficient that a given combination of white ink and color ink satisfies the above-mentioned difference in dynamic surface tension. However, it is preferable that all combinations of white ink and color ink satisfy the above-mentioned difference in dynamic surface tension. The phrase "independently" used above means that the inks 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. By having the ink set satisfy the above-mentioned static surface tension difference and dynamic surface tension difference, the occurrence of color bleeding can be suppressed when white ink is applied to a recording medium and then color ink is applied to the area of the recording medium where the white ink has been applied.

[0011] First, the reason why the occurrence of color bleeding is suppressed in the ink set will be explained. Generally, when printing on a dark-colored recording medium, a white ink is applied to the recording medium to form a white image base, and color inks are then applied to the area where the white ink was applied to improve the color development of the color image. However, if color inks are applied shortly after the white ink is applied (e.g., within 20 seconds), if a large amount of white ink is applied, if the recording medium has low permeability (including non-permeability), or if the color inks are applied without heating the recording medium to which the white ink has been applied by a heating device between the time the white ink is applied and the time the color inks are applied, the white ink may not dry properly, resulting in color bleeding, in which the white ink and the color inks mix together. Note that, similarly to the above, insufficient drying of the white ink may reduce the drying speed of the color inks applied later to the area where the white ink was applied, and beading, which is uneven density in the color image, may also occur. In contrast, by using an ink set including a white ink and a color ink having the above-described relationship between static surface tension and dynamic surface tension, the occurrence of color bleeding can be suppressed even in cases where the white ink may not dry sufficiently.

[0012] Furthermore, when multiple color inks are used in cases where the white ink is not sufficiently dried as described above, in addition to color bleeding, in which the white ink and each color ink mix, color bleeding may also occur in which the color inks come into contact with each other and mix in the area where the white ink is applied. In such a case, the difference in dynamic surface tension between the color inks at 25°C when the bubble lifetime is 15 msec as measured by the maximum bubble pressure method is preferably 1.0 mN / m or less, and more preferably 0.9 mN / m or less. By satisfying the above-mentioned dynamic surface tension difference, color bleeding between the color inks can be suppressed. The above-mentioned dynamic surface tension difference is expressed as an absolute value and is 0 mN / m or more. It is also preferable that the above-mentioned dynamic surface tension difference be satisfied for all combinations of color inks. For example, when black ink, cyan ink, magenta ink, and yellow ink are used as multiple color inks, it is preferable that the above-mentioned dynamic surface tension difference be satisfied for all combinations of black ink and cyan ink, black ink and magenta ink, black ink and yellow ink, cyan ink and magenta ink, cyan ink and yellow ink, and magenta ink and yellow ink. The phrase "independently" used above 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.

[0013] Furthermore, when multiple color inks are used as described above, and the multiple color inks are black ink, cyan ink, magenta ink, and yellow ink, it is preferable that the dynamic surface tension of each ink at 25°C when the bubble lifetime is 15 msec as measured by the maximum bubble pressure method satisfies the following relational expression (1): The more left-side an ink is in relational expression (1) below, the greater the visual impact on the areas of other color inks when color bleed occurs, but by satisfying relational expression (1) below, it is possible to prevent color bleed from occurring, in which the ink on the left side of relational expression (1) invades the ink on the right side.

number

[0014] The static surface tension at 25°C of the white ink and color inks included in the ink set is preferably, independently, 40.0 mN / m or less, more preferably 36.0 mN / m or less, and even more preferably 30.0 mN / m or less. By ensuring that the white ink and color inks satisfy the above static surface tension, it is possible to suppress not only beading between the white ink and color ink, but also beading between different color inks. When multiple white inks or color inks are used, it is sufficient that a given combination of white ink and color ink satisfy the above static surface tension, but it is preferable that all combinations of white ink and color ink satisfy the above static surface tension. Furthermore, the phrase "independently" above means that the white ink and color ink may be the same or different, as long as the static surface tension of the white ink and color ink is 40.0 mN / m or less.

[0015] <White ink and color ink> The white ink and the color inks each contain an organic solvent, water, a colorant, a resin, a surfactant, and other components depending on the purpose. Furthermore, when a pretreatment liquid is used, it is preferable that at least one selected from the colorant and the resin be anionic (these may be collectively referred to as an "anionic compound"). When at least one selected from the colorant and the resin is anionic, the white ink or the color ink aggregates or thickens when it comes into contact with a component (such as a flocculant) contained in the pretreatment liquid, thereby allowing the white ink or the color ink to remain on the surface of the recording medium.

[0016] -Organic solvents- The organic solvent is not particularly limited, but it is preferable to use, for example, one having an equilibrium moisture content of 30% by mass or more in an environment at a temperature of 23°C and a relative humidity of 80% (also called a humectant), and among these, one having a high equilibrium moisture content and a high boiling point is more preferable. The selection of such an organic solvent is related to the suppression of color bleeding and beading (in other words, the control of static surface tension and dynamic surface tension), but is also related to improving the ink ejection stability and suppressing the adhesion of waste ink in the maintenance mechanism of the image forming apparatus. The equilibrium moisture content (%) was calculated by using a saturated aqueous solution of potassium chloride / sodium chloride in a desiccator, maintaining the temperature and humidity at 23°C ± 1°C and a relative humidity of 80% ± 3%, storing petri dishes containing 1g of each organic solvent in the desiccator, measuring the equilibrium moisture content, and calculating it using the following formula. Equilibrium moisture content (mass%) = [amount of moisture absorbed by organic solvent / (amount of organic solvent + amount of moisture absorbed by organic solvent)] x 100

[0017] Examples of humectants include polyhydric alcohols with an equilibrium moisture content of 30% by mass or more in an environment at 23° C. and 80% relative humidity. Specific examples of such polyhydric alcohols include diethylene glycol (bp 245° C., equilibrium moisture content 43% by mass), triethylene glycol (bp 285° C., equilibrium moisture content 39% by mass), tetraethylene glycol (bp 324° C. to 330° C., equilibrium moisture content 37% by mass), 1,3-butanediol (bp 203° C. to 204° C., equilibrium moisture content 35% by mass), glycerin (bp 290° C., equilibrium moisture content 49% by mass), diglycerin (bp 270° C. / 20 hPa, equilibrium moisture content 38% by mass), 1,2,3-butanetriol (bp 175° C. / 33 hPa, equilibrium moisture content 38% by mass), and 1,2,4-butanetriol (bp 190° C. to 191° C. / 24 hPa, equilibrium moisture content 41% by mass). These may be used alone or in combination of two or more. Among these, glycerin and 1,3-butanediol are preferred.

[0018] 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°C), 1,5-pentanediol (bp 242°C), propylene glycol (bp 187°C), 2-methyl-2,4-pentanediol (bp 197°C), ethylene glycol (bp 196°C to 198°C), Examples include propylene 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-hexanetriol (bp 178°C), trimethylolethane (solid, mp 199°C to 201°C), and trimethylolpropane (solid, mp 61°C).

[0019] The organic solvent content of each ink is preferably 10.0% to 75.0% by mass, and more preferably 15.0% to 50.0% by mass. A content of 10.0% by mass or more improves the moisturizing effect of each ink, while a content of 75.0% by mass or less improves the drying properties of each ink on a recording medium.

[0020] When using a recording medium with low permeability (including non-permeability), the organic solvent should have a solubility parameter of 9.0 (J / cm 3 ) 1 / 2 More than 11.8(J / cm 3 ) 1 / 2 It is preferable to use a solvent having a solubility parameter of less than 9.0 (J / cm 3 ) 1 / 2 More than 11.8(J / cm 3 ) 1 / 2 Specifically, the organic solvent having a viscosity of less than 1000 ppm is 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 / cm3 ) 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 ), methyl propylene glycol (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-pentanediol (SP value: 11.80 (J / cm 3 ) 1 / 2 These may be used alone or in combination of two or more.

[0021] Solubility parameter is 9.0 (J / cm 3 ) 1 / 2 More than 11.8(J / cm 3 ) 1 / 2 The content of the organic solvent is preferably from 5.0 to 60.0% by mass, and more preferably from 10.0 to 30.0% by mass, based on the mass of each ink. A content of from 5.0 to 60.0% by mass is preferred from the viewpoint of suppressing color bleeding and beading (in other words, controlling static and dynamic surface tension), and is also preferred from the viewpoint of the color development of each ink.

[0022] It is preferable to adjust the mass ratio of the colorant to the organic solvent appropriately, since this affects the improvement of ink ejection stability, the prevention of waste ink adhesion in the maintenance mechanism of the image forming apparatus, etc. For example, when an ink with a high content of colorant but a low content of organic solvent is ejected from an inkjet head, evaporation of water near the ink meniscus of the nozzle may progress, resulting in ejection defects.

[0023] -water- As the water, for example, pure water such as ion-exchanged water, ultrafiltered water, reverse osmosis water, distilled water, and ultrapure water can be used. The water content in each ink is not particularly limited and can be selected appropriately depending on the purpose. However, from the viewpoint of the drying property and ejection reliability of each ink, the water content is preferably 10.0% by mass or more and 90.0% by mass or less, and more preferably 20.0% by mass or more and 60.0% by mass or less, relative to the mass of each ink.

[0024] -Coloring materials- White ink contains a white colorant, and color ink contains a colorant. In this disclosure, when there is no need to distinguish between white colorant and colorant, they are simply referred to as colorant.

[0025] As the coloring material, a pigment or the like can be used. As the pigment, an inorganic pigment or an organic pigment can be used. These can be used alone or in combination of two or more. As the pigment, for example, a black pigment, a yellow pigment, a magenta pigment, a cyan pigment, a white pigment, a green pigment, an orange pigment, a glossy color pigment such as gold or silver, a metallic pigment, etc. can be used.

[0026] Examples of inorganic pigments include titanium oxide, iron oxide, calcium carbonate, barium sulfate, aluminum hydroxide, barium yellow, cadmium red, chrome yellow, and carbon black. Of 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 the contact method, furnace method, and thermal method.

[0027] Examples of organic pigments include 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 quinophthalone pigments. Examples of dye chelates include basic dye chelates and acid dye chelates.

[0028] Specific examples of organic pigments include CI Pigment Yellow 1, 3, 12, 13, 14, 17, 24, 34, 35, 37, 42 (yellow iron oxide), 53, 55, 74, 81, 83, 95, 97, 98, 100, 101, 104, 408, 109, 110, 117, 120, 128, 139, 150, 151, 155, 153, 180, 183, 185, 213, CI Pigment Orange 5, 13, 16, 17, 36, 43, 51, CI Pigment Red 1, 2, 3, 5, 17, 22, 23, 31, 38, 48:2 (Permanent Red 2B (Ca)), 48:3, 48:4, 49:1, 52:2, 53:1, 57:1 (Brilliant Carmine 6B), 60:1, 63 :1, 63:2, 64:1, 81, 83, 88, 101 (Red Iron), 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, CI Pigment Rhodamine Lake 1 (Rhodamine Lake), 3, 5:1, 16, 19, 23, 38; CI Pigment Blue 1, 2, 15 (Phthalocyanine Blue), 15:1, 15:2, 15:3 (Phthalocyanine Blue), 16, 17:1, 56, 60, 63; CI Pigment Green 1, 4, 7, 8, 10, 17, 18, 36, etc.

[0029] The BET specific surface area of the pigment is 10m 2 / g or more 1500m 2 / g or less is preferable, and 20m 2 / g or more 600m 2 / g or less is more preferable, and 50m 2 / g or more 300m 2 To use a pigment having the desired BET specific surface area, a typical size reduction or grinding treatment (for example, ball milling, jet milling, ultrasonic treatment) may be carried out. Pigment cumulative 50% volume particle size D 50 is preferably 50 nm or more and 350 nm or less in each ink. The pigment content, in solids, is preferably 1.0% to 15.0% by mass, and more preferably 1.5% to 10.0% by mass, of the ink. A content of 1.0% by mass or more improves the color development and image density of each ink, while a content of 15.0% by mass or less stabilizes the ejection properties of each ink.

[0030] The colorant may also be a composite pigment in which organic or inorganic pigment particles are coated with an organic pigment or carbon black. The composite pigment can be prepared by a method in which an organic pigment is precipitated in the presence of inorganic pigment particles, or by a mechanochemical method in which an inorganic pigment and an organic pigment are mechanically mixed and ground. Furthermore, if necessary, a layer of an organosilane compound generated from a polysiloxane and an alkylsilane can be provided between the inorganic pigment and the organic pigment to improve adhesion between them. The mass ratio of the organic pigment or inorganic pigment particles to the organic pigment or carbon black coating them is preferably 3:1 to 1:3, and more preferably 3:2 to 1:2, from the viewpoint of improving color development, coloring power, color tone, and transparency. As composite pigments, silica / carbon black composite material, silica / phthalocyanine PB15:3 composite material, silica / disazo yellow composite material, silica / quinacridone PR122 composite material, and the like, manufactured by Toda Kogyo Co., Ltd., are suitable because they have a small average primary particle size. For example, if inorganic pigment particles with a primary particle diameter of 20 nm are coated with an equal amount of organic pigment, the primary particle diameter of the resulting composite pigment will be approximately 25 nm. If an appropriate dispersant can be used to disperse these particles down to the primary particle size, it will be possible to create a composite pigment dispersion ink with an extremely fine dispersed particle diameter of 25 nm. In composite pigments, the organic pigment on the surface that coats the pigment contributes to dispersion, but the properties of the inorganic pigment at the center also become apparent through the thin layer of organic pigment approximately 2.5 nm thick. Therefore, it is necessary to select a pigment dispersant that can simultaneously stabilize the dispersion of both.

[0031] Furthermore, when a pretreatment liquid is used in addition to the white ink and the color inks in the ink set, as described above, the colorant is preferably anionic, and more preferably an anionic pigment. Examples of anionic pigments include surfactant-dispersed pigments in which a pigment is dispersed in 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 self-dispersed pigments in which hydrophilic groups are provided on the surface of the pigment, and it is preferable that any of these dispersion forms be water-dispersible.

[0032] When the anionic pigment is a resin-coated dispersed pigment or a self-dispersed pigment, it preferably has at least one hydrophilic group on its surface. Examples of hydrophilic groups include -COOM, -SO3M, -PO3HM, -PO3M2, -CONM2, -SO3NM2, -NH-CH4-COOM, -NH-CH4-SO3M, -NH-CH4-PO3HM, -NH-CH4-PO3M2, -NH-CH4-CONM2, and -NH-CH4-SO3NM2. These hydrophilic groups can be introduced by known methods. Furthermore, the counter ion (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. Among these, tetraethylammonium ion, tetrabutylammonium ion, and benzyltrimethylammonium ion are mentioned, with tetrabutylammonium ion being preferred. Inks using such pigments have excellent storage stability over time and suppress an increase in viscosity when water evaporates. This is presumably because the hydrophilic group containing the quaternary ammonium ion allows the pigment dispersion to be kept stable even when water evaporates from a water-rich ink and the ink becomes organic solvent-rich.

[0033] As a colorant other than those having hydrophilic groups on the surface, a polymer emulsion containing a pigment in polymer particles is preferred. The pigment may be encapsulated in the polymer particles or adsorbed on the surface of the polymer particles. In this case, it is not necessary for all the pigment to be encapsulated or adsorbed, and a portion may be dispersed in the emulsion. Examples of polymers for polymer particles include vinyl polymers, polyester polymers, and polyurethane polymers, with vinyl polymers and polyester polymers being preferred.

[0034] -resin- The resin is not particularly limited, but a resin having excellent film-forming properties and solvent resistance, water resistance, and weather resistance is useful in image formation, and examples thereof include condensation-based synthetic resins, addition-based synthetic resins, natural polymer compounds, etc. Furthermore, the resin is preferably a water-dispersible resin (in the form of resin particles). Furthermore, when a pretreatment liquid is used in addition to the white ink and color inks in an ink set, the resin is preferably anionic, as described above.

[0035] Examples of condensation synthetic resins include polyester resins, polyurethane resins, polyepoxy resins, polyamide resins, polyether resins, poly(meth)acrylic resins, acrylic-silicone resins, and fluorine-based resins. Examples of addition-type synthetic resins include polyolefin resins, polystyrene-based resins, polyvinyl alcohol-based resins, polyvinyl ester-based resins, polyacrylic acid-based resins, and unsaturated carboxylic acid-based resins. Examples of natural polymer compounds include celluloses, rosins, and natural rubber. When the ink is applied to a recording medium with low permeability (including non-permeability) such as commercial printing paper or film, it is preferable to use a polyurethane resin in order to improve the fixability of the ink.

[0036] In order to further improve 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). [ka]

[0037] Examples of polyol raw materials having the 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 mass% of the total raw materials for the polyurethane resin, and is preferably about 50 mass% of the total polyol raw materials. When the proportion of the polyol raw material having the structure represented by structural formula (A) is within the above range, alcohol resistance is improved.

[0038] The water-dispersible resin may be one that has self-dispersibility due to the resin itself having a hydrophilic group, or one that does not have dispersibility but has been imparted dispersibility by a surfactant or a resin having a hydrophilic group. Among these, ionomers of polyester resin or polyurethane resin, and emulsions of resin particles obtained by emulsifying and suspension polymerizing unsaturated monomers are preferred. In the case of emulsion polymerization of unsaturated monomers, a resin emulsion is obtained by reacting the unsaturated monomer, a polymerization initiator, a surfactant, a chain transfer agent, a chelating agent, a pH adjuster, and the like in water to which the unsaturated monomer, a polymerization initiator, a surfactant, a chain transfer agent, a chelating agent, a pH adjuster, and the like have been added. This makes it easy to obtain a water-dispersible resin, and it is easy to change the resin composition and to create the desired properties.

[0039] From the viewpoint of suppressing dispersion destruction and scission of molecular chains such as hydrolysis under strong alkaline or strong acidic conditions, the pH of the ink for the water-dispersible resin is preferably 4 to 12. Furthermore, 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.

[0040] The water-dispersible resin functions to fix the water-dispersible colorant to the recording medium, and improves 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 lower. Furthermore, if the glass transition temperature of the water-dispersible resin is −40° C. or lower, the viscosity of the resin film increases and tackiness occurs in the printed matter, so the glass transition temperature is preferably −30° C. or higher. The content of the water-dispersible resin in the ink, in terms of solid content, is preferably 0.5% by mass or more and 20.0% by mass or less, and more preferably 1.0% by mass or more and 15.0% by mass or less, relative to the mass of the ink. On the other hand, when the ink is applied to a recording medium with low permeability (including non-permeability) such as commercial printing paper or film, and a polyurethane resin is used as the resin, the content of the polyurethane resin is 3.0 mass% or more relative to the mass of the ink, and the solid mass ratio of the colorant to the polyurethane resin is preferably 1.0:(2.0 to 12.0), and more preferably 1.0:(2.0 to 11.0).

[0041] -Surfactants- The white ink and the color inks each preferably contain a surfactant as a means for suppressing color bleeding and beading (in other words, controlling static surface tension and dynamic surface tension). Examples of surfactants that can be used include polyether-modified siloxane compounds, acetylene glycol surfactants, and acetylene alcohol surfactants. Furthermore, fluorine-based surfactants, silicone-based surfactants, and the like may be used in combination with the above surfactants. The use of a surfactant makes it difficult for each ink to wet the ink-repellent film on the nozzle plate of the inkjet head, thereby suppressing ejection defects caused by ink adhesion to the nozzles and improving ejection stability.

[0042] The polyether-modified siloxane compounds are preferably those represented by the following general formulas (1) to (5).

[0043] [ka]

[0044] In general formula (1), R represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, m represents an integer of 0 to 23, n represents an integer of 1 to 10, a represents an integer of 1 to 23, and b represents an integer of 0 to 23.

[0045] [ka]

[0046] In general formula (2), R2 and R3 each independently represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, m represents an integer of 1 to 8, and c and d each independently represent an integer of 1 to 10.

[0047] [ka]

[0048] In the general formula (3), R4 represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and e represents an integer of 1 to 8.

[0049] [ka]

[0050] In the general formula (4), R5 represents a polyether group of the following general formula (5), and f represents an integer of 1 to 8.

[0051] [ka]

[0052] In general formula (5), R6 represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, g represents an integer of 0 to 23, and h represents an integer of 0 to 23. However, g and h cannot be 0 at the same time.

[0053] Specific examples of the compound represented by general formula (1) include compounds represented by the following structural formulas (1) to (8).

[0054] [ka]

[0055] [ka]

[0056] [ka]

[0057] [ka]

[0058] [ka]

[0059] [ka]

[0060] [ka]

[0061] [ka]

[0062] Specific examples of the compound represented by general formula (2) include compounds represented by the following structural formula (9).

[0063] [ka]

[0064] Specific examples of the compound represented by general formula (3) include compounds represented by the following structural formula (10).

[0065] [ka]

[0066] Specific examples of the compound represented by general formula (4) include compounds represented by the following structural formulae (11) to (13).

[0067] [ka]

[0068] [ka]

[0069] [ka]

[0070] Further, examples of commercially available polyether-modified siloxane compounds include 71ADDITIVE, 74ADDITIVE, 57ADDITIVE, 8029ADDITIVE, 8054ADDITIVE, 8211ADDITIVE, 8019ADDITIVE, 8526ADDITIVE, FZ-2123, and FZ-2191 manufactured by TORAY Dow Corning; TSF4440, TSF4441, TSF4445, TSF4446, TSF4450, TSF4452, and TSF4460 manufactured by Momentive Performance Materials; Silface SAG002, Silface SAG003, Silface SAG005, Silface SAG503A, Silface SAG008, and Silface SJM003 manufactured by Nissin Chemical Industry Co., Ltd.; and TEGO WetKL245 and TEGO Wet250, TEGO Wet260, TEGO Wet265, TEGO Wet270, TEGO Wet280; BYK-345, BYK-347, BYK-348, BYK-375, BYK-377 manufactured by BYK Japan;

[0071] Furthermore, commercially available products can be used as the acetylene glycol surfactant and the acetylene alcohol surfactant, and examples of commercially available products include Surfynol 104, Surfynol 104E, Surfynol 420, Surfynol 440, 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, Olfine EXP. 4001, Olfine EXP. 4200, Olfine EXP. 4123, and Olfine EXP. 4300 (all manufactured by Nissin Chemical Industry Co., Ltd.).

[0072] The content of the surfactant is preferably 0.001% by mass or more and 5.0% by mass or less, and more preferably 0.5% by mass or more and 3.0% by mass or less, based on the mass of the ink. When the content is 0.001% by mass or more, the effect of adding the surfactant can be obtained. On the other hand, when the content exceeds 5.0% by mass, the effect of adding the surfactant becomes saturated.

[0073] -Other ingredients- As other components, various known additives can be used as needed, such as foam inhibitors (antifoaming agents), pH adjusters, antiseptics and antifungals, chelating agents, rust inhibitors, antioxidants, ultraviolet absorbers, oxygen absorbers, and light stabilizers.

[0074] --Foam suppressor-- Foam suppressors are added in minute amounts to ink to suppress ink foaming. Foaming refers to a liquid forming a thin film that encases air. The formation of this foam is influenced by ink characteristics such as surface tension and viscosity. Liquids with high surface tension, such as water, are less likely to foam because of the forces that try to minimize the surface area of the liquid. In contrast, inks with high viscosity and high permeability tend to foam easily because of their low surface tension, and the generated foam tends to be maintained due to the viscosity of the solution, making it difficult to eliminate. Typically, foam suppressors destroy bubbles by locally lowering the surface tension of the foam film, or by dotting the surface of the foaming liquid with foam suppressors that are insoluble in the foaming liquid. When a polyether-modified siloxane compound, which acts as a surfactant and has a very strong effect of lowering surface tension, is used in the ink, the surface tension of the foam film cannot be locally lowered even with the use of a foam suppressor that works by the former mechanism. Therefore, it is preferable to use a foam suppressor that is insoluble in the foaming liquid. However, in this case, the stability of the ink may be reduced by the foam suppressor that is insoluble in the solution. In contrast, the foam suppressor represented by the following general formula (6) does not have as strong an effect of reducing surface tension as the polyether-modified siloxane compound, but it is highly compatible with the polyether-modified siloxane compound. For this reason, the foam suppressor is efficiently incorporated into the foam film, and the difference in surface tension between the polyether-modified siloxane compound and the foam suppressor causes the surface of the foam film to become locally unbalanced, which is thought to cause the foam to collapse.

[0075] [ka]

[0076] In the general formula (6), R7 and R8 each independently represent an alkyl group having 3 to 6 carbon atoms; R9 and R 10 each independently represents an alkyl group having 1 to 2 carbon atoms, and n represents an integer of 1 to 6.

[0077] Examples of the compound represented by general formula (6) include 2,4,7,9-tetramethyldecane-4,7-diol and 2,5,8,11-tetramethyldodecane-5,8-diol. Among these, 2,5,8,11-tetramethyldodecane-5,8-diol is preferred due to its high anti-foaming effect and compatibility with ink. The content of the anti-foaming agent is preferably 0.01% to 10.0% by mass, and more preferably 0.1% to 5.0% by mass, relative to the mass of the ink. A content of 0.01% by mass or more provides a foam-suppressing effect, while a content of 10% by mass or less can suppress any effects on ink properties such as viscosity and particle size.

[0078] --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 depending on the purpose, and examples include alcohol amines, hydroxides of alkali metal elements, hydroxides of ammonium, phosphonium hydroxides, and carbonates of alkali metals. The pH of the ink is preferably 7 to 11 from the viewpoint of improving the ejection stability of the ink.

[0079] Examples of alcohol amines include diethanolamine, triethanolamine, and 2-amino-2-ethyl-1,3 propanediol. Examples of hydroxides of alkali metal elements include lithium hydroxide, sodium hydroxide, and potassium hydroxide. Examples of ammonium hydroxides include ammonium hydroxide and quaternary ammonium hydroxides. Examples of the phosphonium hydroxide include quaternary phosphonium hydroxide. Examples of alkali metal carbonates include lithium carbonate, sodium carbonate, and potassium carbonate.

[0080] --Preservative and fungicidal agent-- Examples of antiseptic and antifungal agents include sodium dehydroacetate, sodium sorbate, sodium 2-pyridinethiol-1-oxide, sodium benzoate, and sodium pentachlorophenol.

[0081] --Chelating reagents-- Examples of chelating agents include sodium ethylenediaminetetraacetate, sodium nitrilotriacetate, sodium hydroxyethylethylenediaminetriacetate, sodium diethylenetriaminepentaacetate, and sodium uramildiacetate.

[0082] --Rust inhibitor-- Examples of the rust inhibitor include acid sulfite, sodium thiosulfate, ammonium thiodiglycolate, diisopropylammonium nitrite, pentaerythritol tetranitrate, and dicyclohexylammonium nitrite.

[0083] --Antioxidants-- Examples of antioxidants include phenol-based antioxidants (including hindered phenol-based antioxidants), amine-based antioxidants, sulfur-based antioxidants, and phosphorus-based antioxidants.

[0084] --UV absorber-- Examples of ultraviolet absorbers include benzophenone-based ultraviolet absorbers, benzotriazole-based ultraviolet absorbers, salicylate-based ultraviolet absorbers, cyanoacrylate-based ultraviolet absorbers, and nickel complex salt-based ultraviolet absorbers.

[0085] -Physical properties of each ink- The physical properties of each ink are not particularly limited and can be appropriately selected depending on 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, and more preferably 6 mPa·s or more and 20 mPa·s or less. A viscosity of 5 mPa·s or more improves image density and character quality. A viscosity of 25 mPa·s or less improves ink ejection properties. The viscosity can be measured at 25°C using, for example, a viscometer (RE-85L, manufactured by Toki Sangyo Co., Ltd.).

[0086] - Manufacturing methods for 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 resulting mixture at a temperature of 40° C. or higher but lower than 70° C. for 6 hours or longer. This stirring and mixing can be carried out using, for example, a sand mill, a homogenizer, a ball mill, a paint shaker, an ultrasonic disperser, or the like.

[0087] <Pretreatment liquid> The pretreatment liquid contains a flocculant, and optionally contains resin particles, wax particles, an organic solvent, water, a surfactant, and other components.

[0088] -Flocculant- In this disclosure, the term "aggregating agent" refers to a component that causes aggregation or thickening of the white ink or color ink when the pretreatment liquid comes into contact with the white ink or color ink. Specific examples of such components include components that cause aggregation of water-dispersible particles (e.g., the anionic compounds described above) such as coloring materials or resins contained in the white ink or color ink. By using a pretreatment liquid containing such an aggregating agent, aggregation or thickening occurs in the white ink or color ink that comes into contact with the pretreatment liquid, thereby allowing the white ink or color ink to remain on the surface of the recording medium. The flocculant may be a cationic compound, such as an inorganic metal salt, an organic acid metal salt, an organic acid ammonium salt, or a cationic polymer.

[0089] 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 bicarbonate, potassium bicarbonate, sodium chloride, and potassium chloride.

[0090] 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, calcium citrate, tripotassium citrate, trisodium citrate, disodium citrate, zinc lactate, aluminum lactate, potassium lactate, calcium lactate, sodium lactate, magnesium lactate, calcium acetate, potassium tartrate, calcium tartrate, DL-sodium tartrate, and potassium sodium tartrate.

[0091] The inorganic metal salt and organic acid metal salt are preferably at least one selected from calcium salts, magnesium salts, nickel salts, and aluminum salts. These salts improve the aggregation function of water-dispersible particles contained in the white ink or color ink, further suppressing the occurrence of color bleeding and beading. They are also preferred from the viewpoint of the storage stability of the pretreatment liquid.

[0092] Examples of 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 ammonium L-glutamate.

[0093] As the cationic polymer, for example, a quaternary ammonium salt type cationic polymer compound is preferable, and specific examples thereof include dialkylallylammonium chloride polymers, dialkylaminoethyl (meth)acrylate quaternary ammonium salt polymers, modified polyvinyl alcohol dialkylammonium salt polymers, and dialkyldiallylammonium salt polymers. Other cationic polymers include cationic specially modified polyamine compounds, cationic polyamide polyamine compounds, cationic urea-formalin resin compounds, cationic polyacrylamide compounds, cationic alkyl ketene dimers, cationic dicyandiamide compounds, cationic dicyandiamide-formalin condensation compounds, cationic dicyandiamide-polyamine condensation compounds, cationic polyvinyl formamide compounds, cationic polyvinyl pyridine compounds, cationic polyalkylene polyamine compounds, and cationic epoxy polyamide compounds. Particularly preferred cationic polymers include compounds represented by the following general formulas (7) to (9).

[0094] [ka]

[0095] In general formula (7), R 10 represents a methyl group or an ethyl group, and Y - represents a halogen ion, and n represents an integer.

[0096] [ka]

[0097] In general formula (8), Y - represents a halogen ion, a nitrate ion, a nitrite ion, or an acetate ion, and R 11 represents H or CH3, R 12 , R 13 , and R 14 each independently represents H or an alkyl group, and n represents an integer.

[0098] [ka]

[0099] In the general formula (9), R represents a methyl group or an ethyl group, and Y - represents a halogen ion, a nitrate ion, a nitrite ion, or an acetate ion, and n represents an integer.

[0100] From the viewpoint of the solubility of the flocculant and the like and from the viewpoint of suppressing the occurrence of color bleeding and beading, the content of the flocculant is preferably from 0.1% by mass to 30.0% by mass, and more preferably from 1.0% by mass to 20.0% by mass, relative to the mass of the pretreatment liquid.

[0101] -Resin particles- The pretreatment liquid preferably contains resin particles, which can improve the adhesion between the white ink and the color ink and the recording medium.

[0102] Since the resin particles coexist with a cationic compound flocculant in the pretreatment solution, from the viewpoint of long-term storage stability, it is preferable to use nonionic resin particles dispersed by steric hindrance rather than the commonly used charge-repellent emulsion. When anionic resin particles, which are charge-repellent emulsions, are used, aggregation occurs when they coexist with inorganic metal salts, which are an example of flocculants. In particular, aggregation occurs instantly when they coexist with polyvalent metal salts, which generate trivalent cations upon dissociation. Furthermore, when cationic resin particles are used, they are sufficiently stable when left at room temperature, but thickening occurs when they are left standing at elevated temperatures as an accelerated test for long-term stability. Therefore, as mentioned above, it is preferable that the resin particles be nonionic resin particles. There are no particular limitations on the method for determining whether resin particles are nonionic resin particles. For example, a method may be used in which the solid content is isolated from the pretreatment liquid by centrifugation, and then a pyrolysis GC-MS (e.g., GC-17A manufactured by Shimadzu Corporation) is used to demonstrate that no material containing acidic functional groups such as carboxyl groups and sulfo groups, or basic functional groups such as amino groups, is detected.

[0103] Examples of nonionic resin particles that can be used include polyolefin resins, chlorinated polyolefin resins, polyvinyl acetate resins, polyvinyl chloride resins, polyester resins, polyurethane resins, acrylic resins, styrene-butadiene resins, and copolymers of polymerizable compounds used in the polymerization of these resins. Ethylene-vinyl acetate copolymer resins, ethylene-vinyl acetate-vinyl chloride copolymer resins, and chlorinated olefin resins are more preferred. These resins can further improve the adhesion between white ink and color inks and recording media.

[0104] The glass transition temperature (Tg) of the nonionic resin particles is preferably −30° C. or higher and 30° C. or lower, and more preferably −25° C. or higher and 25° C. or lower. A temperature of −30° C. or higher makes the resin film stronger, and the layer formed by the pretreatment liquid becomes more robust. Furthermore, a temperature of 30° C. or lower improves the film-forming properties of the resin and ensures flexibility, thereby further improving the adhesion between the white ink and color ink and the recording medium.

[0105] The content (solid content) of the resin particles is preferably 0.5% by mass or more and 20.0% by mass or less relative to the mass of the pretreatment liquid, which can further improve the adhesion between the white ink and the color ink and the recording medium.

[0106] -Wax particles- The wax particles are not particularly limited, and a water-dispersible wax or the like can be used. Specific examples include plant- and animal-based waxes such as carnauba wax, candelilla wax, beeswax, rice wax, and lanolin; petroleum-based waxes such as paraffin wax, microcrystalline wax, polyethylene wax, polypropylene wax, oxidized polyethylene wax, and petrolatum; mineral waxes such as montan wax and ozokerite; and synthetic waxes such as carbon wax, Hoechst wax, polyethylene wax, and stearic acid amide. Among these, paraffin wax and polyethylene wax are preferred from the viewpoint of further improving the adhesion between the white ink and color ink and the recording medium and from the viewpoint of dispersibility in the pretreatment liquid.

[0107] The melting point of the wax particles is preferably 50° C. or higher and 130° C. or lower, and more preferably 60° C. or higher and 120° C. or lower. When the melting point is within the above range, the adhesion between the white ink and the color ink and the recording medium can be further improved.

[0108] The wax content (solid content) is preferably 0.05% by mass or more and 5.0% by mass or less, and more preferably 0.1% by mass or more and 3.0% by mass or less, relative to the mass of the pretreatment liquid. A wax content of 0.05% by mass or more and 5.0% by mass or less allows the white ink to remain near the surface of the recording medium, thereby improving Hunter brightness. However, if a white ink layer is formed after applying a pretreatment liquid containing wax and then an image is formed on the white ink layer using color inks, color bleeding may be more likely to occur than with a pretreatment liquid that does not contain wax.

[0109] -Organic solvents- The organic solvent is not particularly limited, and a water-soluble organic solvent can be used, for example, polyhydric alcohols, ethers such as polyhydric alcohol alkyl ethers and polyhydric alcohol aryl ethers, nitrogen-containing heterocyclic compounds, amides, amines, and sulfur-containing compounds.

[0110] Specific examples of the water-soluble organic solvent include 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-butanediol, triethylene glycol, polyethylene glycol, polypropylene glycol, 1,2-pentanediol, 1,3-pentanediol, 1,4-pentanediol, 2,4-pentanediol, 1,5-pentanediol, and the like. Polyhydric alcohols such as 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 petriol, ethylene glycol monoethyl ether, and ethylene glycol monobutyl ether. polyhydric alcohol alkyl ethers such as diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, and propylene glycol monoethyl ether; polyhydric alcohol aryl ethers such as ethylene glycol monophenyl ether and ethylene glycol monobenzyl ether; nitrogen-containing heterocyclic compounds such as 2-pyrrolidone, N-methyl-2-pyrrolidone, N-hydroxyethyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, ε-caprolactam, and γ-butyrolactone; amides such as formamide, N-methylformamide, N,N-dimethylformamide, 3-methoxy-N,N-dimethylpropionamide, and 3-butoxy-N,N-dimethylpropionamide; amines such as monoethanolamine, diethanolamine, and triethylamine; sulfur-containing compounds such as dimethyl sulfoxide, sulfolane, and thiodiethanol; propylene carbonate; and ethylene carbonate. It is preferable to use an organic solvent having a boiling point of 250° C. or less, since it not only functions as a wetting agent but also provides good drying properties. Furthermore, it is preferable that the organic solvent contains at least one selected from 1,2-propanediol, 1,3-butanediol, and 1,2-butanediol, since this makes it easier to wet the surface of the recording medium.

[0111] The content of the organic solvent is not particularly limited and can be appropriately selected depending on the purpose. From the viewpoint of the drying property and ejection reliability of the pretreatment liquid, the content is preferably from 5.0% by mass to 60.0% by mass, and more preferably from 10.0% by mass to 30.0% by mass, based on the mass of the pretreatment liquid.

[0112] -water- As the water, for example, pure water such as ion-exchanged water, ultrafiltered water, reverse osmosis water, distilled water, and ultrapure water can be used. The water content in the pretreatment liquid is not particularly limited and can be appropriately selected depending on the purpose. From the viewpoint of the drying properties of the pretreatment liquid, the water content is preferably from 10.0% by mass to 90.0% by mass, and more preferably from 20.0% by mass to 60.0% by mass.

[0113] -Surfactants- As the surfactant, any of silicone surfactants, fluorine surfactants, amphoteric surfactants, nonionic surfactants and anionic surfactants can be used.

[0114] The silicone 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 preferred, for example, side chain modified polydimethylsiloxane, both end modified polydimethylsiloxane, one end modified polydimethylsiloxane, side chain both end modified polydimethylsiloxane, etc., and those having a polyoxyethylene group or a polyoxyethylene polyoxypropylene group as a modifying group are particularly preferred because they exhibit good properties as aqueous surfactants.In addition, polyether modified silicone surfactants can also be used as the silicone surfactant, for example, compounds in which a polyalkylene oxide structure is introduced into the Si part side chain of dimethylsiloxane, etc.

[0115] Preferred fluorosurfactants, for example, are perfluoroalkyl sulfonic acid compounds, perfluoroalkyl carboxylic acid compounds, perfluoroalkyl phosphate ester compounds, perfluoroalkyl ethylene oxide adducts, and polyoxyalkylene ether polymer compounds having perfluoroalkyl ether groups in their side chains, due to their low foaming properties. Examples of perfluoroalkyl sulfonic acid compounds include perfluoroalkyl sulfonic acid and perfluoroalkyl sulfonate salts. Examples of perfluoroalkyl carboxylic acid compounds include perfluoroalkyl carboxylic acids and perfluoroalkyl carboxylate salts. Examples of polyoxyalkylene ether polymer compounds having perfluoroalkyl ether groups in their side chains include sulfate salts of polyoxyalkylene ether polymers having perfluoroalkyl ether groups in their side chains, and salts of polyoxyalkylene ether polymers having perfluoroalkyl ether groups in their side chains. Examples of counterions of the salts in these fluorosurfactants include Li, Na, K, NH, NHCHCHOH, NH(CHCHOH), NH(CHCHOH), and the like.

[0116] Examples of amphoteric surfactants include lauryl aminopropionate, lauryl dimethyl betaine, stearyl dimethyl betaine, and lauryl dihydroxyethyl betaine.

[0117] Examples of nonionic surfactants include polyoxyethylene alkylphenyl ethers, polyoxyethylene alkyl esters, polyoxyethylene alkylamines, polyoxyethylene alkylamides, polyoxyethylene propylene block polymers, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, and ethylene oxide adducts of acetylene alcohol.

[0118] Examples of anionic surfactants include polyoxyethylene alkyl ether acetates, dodecylbenzenesulfonates, laurates, and salts of polyoxyethylene alkyl ether sulfates.

[0119] -Other ingredients- Other components may include, as required, an antifoaming agent, an antiseptic / fungal agent, an antirust agent, and the like.

[0120] --Antifoaming agent-- The antifoaming agent is not particularly limited, and examples thereof include silicone-based antifoaming agents, polyether-based antifoaming agents, and fatty acid ester-based antifoaming agents. These may be used alone or in combination of two or more. Among these, silicone-based antifoaming agents are preferred because of their excellent foam-breaking effect.

[0121] --Preservative and fungicidal agent-- The antiseptic and antifungal agent is not particularly limited, and examples thereof include 1,2-benzisothiazolin-3-one.

[0122] --Rust inhibitor-- The rust inhibitor is not particularly limited, and examples thereof include 1,2,3-benzotriazole, acid sulfite, and sodium thiosulfate.

[0123] <Recording Media> The recording medium to which the white ink, color ink, and pretreatment liquid are applied is not particularly limited and can be appropriately selected depending on the purpose. Examples include plain paper, glossy paper, special paper, fabric, film, OHP sheet, and general-purpose printing paper. Among these, low-permeability recording media such as commercial printing paper, non-permeable recording media for signage, and fabric are preferred, as they are prone to color bleeding and beading and the effects obtained by applying the ink set of the present disclosure are more pronounced. Note that, unlike film and paper, fabric has a surface structure rich in irregularities, and therefore is a recording medium to which a large amount of white ink and color ink is applied, making color bleeding and beading more likely to occur.

[0124] Fabric will be described as an example of a recording medium. In this disclosure, "fabric" refers to fibers in the form of woven fabric, knitted fabric, nonwoven fabric, or the like. The fibers are preferably organic fibers such as synthetic fibers, semi-synthetic fibers, regenerated fibers, and natural fibers. Examples of synthetic fibers include polyester, polyamide, acrylic, polyolefin, polyvinyl alcohol, polyvinyl chloride, polyurethane, and polyimide. Examples of semi-synthetic fibers include acetate, diacetate, and triacetate. Examples of regenerated fibers include polynosic, rayon, lyocell, and cupra. Examples of natural fibers include cotton, linen, silk, and wool. Among the fibers that form fabrics, synthetic fibers such as polyester are more prone to color bleeding and beading than natural fibers such as cotton, and it is also more difficult to retain white ink on the surface. However, the ink set of the present disclosure works well on such fabrics, suppressing color bleeding and beading, and also making it possible for the white ink to remain on the surface.

[0125] The fabric is preferably dark in color, with the fibers used in the fabric being colored by chemically or physically retaining a colorant such as a pigment or dye inside or on the surface. When the fabric is dark in color, a white base may be formed between the fabric and the color image in order to improve the color development of the color image formed on the fabric. This makes it preferable to use an ink set having the white ink and color ink of the present disclosure. In addition, in the present disclosure, "dark color fabric" refers to a fabric having a lightness (L * ) using a spectrophotometer (e.g., X-rite exact (manufactured by X-rite)), 60>L * It represents fabrics that meet the range of 50>L * It is preferable that the fabric satisfies the range of 40>L * It is more preferable that the fabric satisfies the range of 30>L * It is more preferable that the fabric satisfies the range of 20>L * It is particularly preferable that the fabric satisfies the range.

[0126] <<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 inks, a white ink application unit that applies the white ink to a recording medium, and a color ink application unit that applies the color ink to the area of the recording medium to which the white ink has been applied, and may include other components as necessary. Examples of other components include a pretreatment liquid storage unit that stores a pretreatment liquid, a pretreatment liquid application unit that applies the pretreatment liquid to the recording medium, and a heating unit that heats various liquids such as the white ink, color ink, or pretreatment liquid that have been applied to the recording medium. Note that when the image forming apparatus includes a pretreatment liquid storage unit and a pretreatment liquid application unit, the white ink application unit can be rephrased as a unit that applies the white ink to the area of the recording medium to which the pretreatment liquid has been applied. 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 inks to the areas of the recording medium to which the white ink has been applied, and may include other steps as necessary. Examples of other steps include a pretreatment liquid application step of applying a pretreatment liquid to the areas of the recording medium to which the white ink has been applied before the white ink application step, and a heating step of heating various liquids such as the white ink, color inks, or pretreatment liquid that have been applied to the recording medium. Note that 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 areas of the recording medium to which the pretreatment liquid has been applied.

[0127] <Image forming device> An image forming apparatus will be described with reference to Figures 1 and 2. Figure 1 is a schematic diagram showing an example of an image forming apparatus. Figure 2 is a schematic diagram showing an example of a storage unit (white ink storage unit, color ink storage unit, or pretreatment liquid storage unit).

[0128] The image forming apparatus 400 shown in FIG. 1 is an image forming apparatus having a serial inkjet head. A mechanism unit 420 is provided inside an exterior 401 of the image forming apparatus 400. Storage units 411 in a pretreatment liquid storage unit 410p for pretreatment liquid, a white ink storage unit 410w for white ink, a black ink storage unit 410k for black ink, and a cyan ink storage unit 410c for cyan ink are formed of a packaging material such as an aluminum laminate film. The storage units 411 are stored in a storage container case 414 made of, for example, plastic. As a result, each storage unit 410 is used as a cartridge.

[0129] On the other hand, a cartridge holder 404 is provided at the back side of the opening when the cover 401c of the apparatus main body is opened. Each storage unit 410 is detachably attached to the cartridge holder 404. This allows the discharge port 413 of each storage unit 410 to communicate with the inkjet ejection head 434 via each supply tube 436, making it possible to eject the pretreatment liquid and each ink from the inkjet ejection head 434 onto a recording medium. 1, the pretreatment liquid is applied to the recording medium by an inkjet ejection method, but the method for applying the pretreatment liquid is not limited to this. For example, the pretreatment liquid may be applied by a blade coating method, a roll coating method, a spray coating method, or the like.

[0130] The image forming apparatus 400 may include a heating unit that heats various liquids, such as the white ink, color inks, or pretreatment liquid, applied to the recording medium. However, it is preferable that the image forming apparatus 400 does not include a heating unit that heats the recording medium to which the white ink has been applied between the application of the white ink and the application of the color inks. Such a heating unit is provided for the purpose of heating and drying the white ink to suppress color bleeding and beading that occur due to insufficient drying of the white ink. However, the ink set of the present disclosure can suppress color bleeding and beading even without a heating unit. Examples of the heating unit include known heating units such as a roll heater, a drum heater, a hot air generator, and a heat press.

[0131] <Image forming method> In the image forming method, examples of the application methods in the white ink application step, color ink application step, and pretreatment liquid application step are each independently a discharge method, a coating method, etc. The white ink application step and color ink application step are preferably a discharge method, and more preferably an inkjet discharge method.

[0132] The ejection method is not particularly limited and can be selected appropriately depending on the purpose. Examples include a method using a piezoelectric element actuator, a method using thermal energy, a method using an actuator that utilizes electrostatic force, and a method using a continuous-jet charge-control type head.

[0133] 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, smoothing coating, microgravure coating, reverse roll coating, four- to five-roll coating, dip coating, curtain coating, slide coating, and die coating.

[0134] The image forming method may include a heating step in which various liquids, such as white ink, color inks, or pretreatment liquid, applied to the recording medium are heated, but it is preferable that the method does not include a heating step in which the recording medium to which the white ink has been applied is heated between the white ink application step and the color ink application step. Such a heating step is provided for the purpose of heating and drying the white ink to suppress color bleeding and beading that occur due to insufficient drying of the white ink, but the ink set of the present disclosure can suppress color bleeding and beading without including a heating step. Furthermore, in the image forming method, the time from when the white ink is applied to the recording medium until the color ink is applied to the area of the recording medium where the white ink has been applied is preferably within 20 seconds. This time is the time required for the white ink to dry, and in view of the purpose of suppressing color bleeding and beading caused by insufficient drying of the white ink, a time longer than 20 seconds is generally preferred, but this is because the ink set of the present disclosure can suppress color bleeding and beading even if the time is within 20 seconds.

[0135] 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. For example, from the viewpoint of improving image quality and drying properties, it is 1 g / m 2 More than 500g / m 2 Preferably, it is 5 g / m or less. 2 More than 400g / m 2 When a fabric is used as the recording medium, it is more preferable that the density is 50 g / m or less. 2 More than 500g / m 2 It is preferable that the density is 100 g / m or less. 2 More than 400g / m 2 More preferably, it is 150 g / m or less. 2 More than 300g / m 2 It is more preferable that:

[0136] The amount of color ink applied to the recording medium in the color ink application process varies greatly depending on the type of recording medium. For example, from the viewpoint of improving image quality and drying properties, it is preferable to apply 1 g / m 2 More than 50g / m 2 Preferably, it is 5 g / m or less. 2 More than 30g / m 2 When a fabric is used as the recording medium, it is more preferable that the density is 5 g / m or less. 2 More than 50g / m 2 Preferably, it is 10 g / m or less. 2 More than 30g / m 2 More preferably, it is:

[0137] The amount of pretreatment liquid applied to the recording medium in the pretreatment liquid application step varies greatly depending on the type of recording medium. For example, from the viewpoint of improving image quality and drying properties, it is preferable to apply 0.1 g / m 2 More than 500g / m 2 It is preferable that the content is less than 1 g / m 2 More than 400g / m 2 When a fabric is used as the recording medium, it is more preferable that the density is 100 g / m or less. 2 More than 500g / m 2 Preferably, it is 200 g / m or less.2 More than 500g / m 2 More preferably, it is 300 g / m or less. 2 More than 400g / m 2 It is more preferable that: [Example]

[0138] Examples of the present invention will be described below, but the present invention is not limited to these examples in any way.

[0139] <Example of pigment dispersion preparation> -Preparation Example 1: Preparation of surface-modified black pigment dispersion- Cabot Corporation's Black Pearls (registered trademark) 1000 (BET specific surface area 343 m 2 100 g of carbon black (carbon black with a dibutyl phthalate absorption capacity of 105 mL / 100 g, dibutyl phthalate absorption capacity (DBPA) of 105 mL / 100 g), 100 mmol of sulfanilic acid, and 1 L of ion-exchanged high-purity water were mixed at room temperature in a Silverson mixer (6,000 rpm). Next, 100 mmol of nitric acid was added to the resulting slurry, and after a further 30 minutes, sodium nitrite (100 mmol) dissolved in 10 mL of ion-exchanged high-purity water was slowly added. The mixture was then heated to 60°C with stirring and reacted for 1 hour to obtain a modified pigment in which sulfanilic acid was attached to carbon black. Next, the pH was adjusted to 9 with a 10% by mass tetrabutylammonium hydroxide solution (methanol solution), and after 30 minutes, a modified pigment dispersion was obtained. Next, this dispersion and ion-exchanged high-purity water were subjected to ultrafiltration using a dialysis membrane, and further ultrasonic dispersion was performed to obtain a surface-modified black pigment dispersion containing 20% by mass of pigment solids. The surface treatment level of the pigment in the obtained surface-modified black pigment dispersion was 0.75 mmol / g, and when measured using a particle size distribution analyzer (Nanorakku UPA-EX150, manufactured by Nikkiso Co., Ltd.), the cumulative 50% volume particle diameter D 50 was 120 nm.

[0140] -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 subjected to acid precipitation with a 0.1 N HCl aqueous solution. Next, the pH was adjusted to 9 with a 10% by mass aqueous solution of tetraethylammonium hydroxide, and after 30 minutes, a modified pigment dispersion was obtained. The modified pigment dispersion containing a pigment bonded to at least one aminobenzoic acid group or aminobenzoic acid tetraethylammonium salt and ion-exchanged highly pure water were subjected to ultrafiltration using a dialysis membrane, and further ultrasonic dispersion was performed to obtain a surface-modified magenta pigment dispersion containing 20% by mass of pigment solids. The obtained surface-modified magenta pigment dispersion was measured using a particle size distribution analyzer (Nanorakku UPA-EX150, manufactured by Nikkiso Co., Ltd.). The cumulative 50% volume particle diameter D 50 was 104 nm.

[0141] -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 subjected to acid precipitation with a 0.1 N HCl aqueous solution. Next, the pH was adjusted to 9 with a 40% by mass benzyltrimethylammonium hydroxide solution (methanol solution), and after 30 minutes, a modified pigment dispersion was obtained. The modified pigment dispersion containing a pigment bonded to at least one aminobenzoic acid group or aminobenzoic acid benzyltrimethylammonium salt and ion-exchanged high-purity water were subjected to ultrafiltration using a dialysis membrane, and further ultrasonic dispersion was performed to obtain a surface-modified cyan pigment dispersion containing 20% by mass of pigment solids. The obtained surface-modified cyan pigment dispersion was measured using a particle size distribution analyzer (Nanotrac UPA-EX150, manufactured by Nikkiso Co., Ltd.). The cumulative 50% volume particle diameter D 50 was 116 nm.

[0142] -Preparation Example 4: Preparation of Surface-Modified Yellow Pigment Dispersion- 1 kg of SENSIENT SMART Yellow 3074BA pigment dispersion (surface-treated Pigment Yellow 74 dispersion, pigment solids content 14.5% by mass) was adjusted to pH 9 with a 10% by mass tetrabutylammonium hydroxide solution (methanol solution), and left for 30 minutes to yield a modified pigment dispersion. The modified pigment dispersion, containing a pigment bonded to at least one aminobenzoic acid group or aminobenzoic acid tetrabutylammonium salt, and high-purity ion-exchange water were subjected to ultrafiltration using a dialysis membrane, followed by ultrasonic dispersion to yield a surface-modified yellow pigment dispersion containing 20% pigment solids. The obtained surface-modified yellow pigment dispersion was measured using a particle size distribution analyzer (Nanotrac UPA-EX150, manufactured by Nikkiso Co., Ltd.). The cumulative 50% volume particle diameter D 50 was 145 nm.

[0143] -Preparation Example 5: Preparation of magenta pigment-containing polymer particle dispersion- After thoroughly replacing the air in a 1 L flask equipped with a mechanical stirrer, thermometer, nitrogen gas inlet tube, reflux condenser, and dropping funnel with nitrogen, 11.2 g of styrene, 2.8 g of acrylic acid, 12.0 g of lauryl methacrylate, 4.0 g of polyethylene glycol methacrylate, 4.0 g of styrene macromer, and 0.4 g of mercaptoethanol were mixed in the flask and heated to 65 ° C. Next, a mixed solution of 100.8 g of styrene, 25.2 g of acrylic acid, 108.0 g of lauryl methacrylate, 36.0 g of polyethylene glycol methacrylate, 60.0 g of hydroxylethyl methacrylate, 36.0 g of styrene macromer, 3.6 g of mercaptoethanol, 2.4 g of azobismethylvaleronitrile, and 18 g of methyl ethyl ketone was added dropwise to the flask over 2.5 hours. After the dropwise addition, a mixed solution of 0.8 g of azobismethylvaleronitrile and 18 g of methyl ethyl ketone was added dropwise to the flask over 0.5 hours. After stirring at 65°C for 1 hour, 0.8 g of azobismethylvaleronitrile was added and stirred for another 1 hour. After the reaction was completed, 364 g of methyl ethyl ketone was added to the flask, yielding 800 g of polymer solution A with a concentration of 50% by mass. Next, 28 g of polymer solution A, 42 g of CI Pigment Red 122, 13.6 g of 1 mol / L potassium hydroxide aqueous solution, 20 g of methyl ethyl ketone, and 13.6 g of ion-exchanged water were thoroughly stirred and then kneaded using a roll mill. The resulting paste was added to 200 g of pure water and thoroughly stirred. After that, the methyl ethyl ketone and water were distilled off using an evaporator. Furthermore, to remove coarse particles, the resulting dispersion was pressure-filtered through a polyvinylidene fluoride membrane filter with an average pore size of 5.0 μm, yielding a magenta pigment-containing polymer microparticle dispersion containing 15% pigment by mass and 20% solids by mass. The obtained magenta pigment-containing polymer particle dispersion was measured using a particle size distribution analyzer (Nanotrac UPA-EX150, manufactured by Nikkiso Co., Ltd.). The cumulative 50% volume particle diameter D 50 was 127 nm.

[0144] -Preparation Example 6: Preparation of cyan pigment-containing polymer particle dispersion- A cyan pigment-containing polymer fine particle dispersion was prepared in the same manner as in Preparation Example 5, except that CI Pigment Red 122 used in Preparation Example 5 was changed to a phthalocyanine pigment (CI Pigment Blue 15:3). The polymer particles in the obtained cyan pigment-containing polymer particle dispersion were measured using a particle size distribution analyzer (Nanotrac UPA-EX150, manufactured by Nikkiso Co., Ltd.). The cumulative 50% volume particle diameter D 50 was 93 nm.

[0145] -Preparation Example 7: Preparation of yellow pigment-containing polymer particle dispersion- A yellow pigment-containing polymer fine particle dispersion was prepared in the same manner as in Preparation Example 5, except that CI Pigment Red 122 used in Preparation Example 5 was changed to a bisazo yellow pigment (CI Pigment Yellow 155). The polymer particles in the obtained yellow pigment-containing polymer particle dispersion were measured using a particle size distribution analyzer (Nanotrac UPA-EX150, manufactured by Nikkiso Co., Ltd.). The cumulative 50% volume particle diameter D 50 was 76 nm.

[0146] -Preparation Example 8: Preparation of Black Pigment-Containing Polymer Microparticle Dispersion- A black pigment-containing polymer fine particle dispersion was prepared in the same manner as in Preparation Example 5, except that CI Pigment Red 122 used in Preparation Example 5 was changed to carbon black (FW100, manufactured by Degussa). The polymer particles in the obtained black pigment-containing polymer particle dispersion were measured using a particle size distribution analyzer (Nanotrac UPA-EX150, manufactured by Nikkiso Co., Ltd.). The cumulative 50% volume particle diameter D 50 was 104 nm.

[0147] -Preparation Example 9: Preparation of polymer-dispersed white pigment dispersion- 55.6 g of DISPERBYK-2081 (BYK Japan) copolymer solution, 517 g of titanium oxide (TITONE R-25, Sakai Chemical Industry Co., Ltd.), 50 g of β-methoxy-N,N-dimethyl-propionamide, and 377.4 g of ion-exchanged water were thoroughly stirred and then placed in a bead mill (Dyno Mill) to measure the cumulative 50% volume particle diameter D 50 Dispersion was continued until the particle size reached 300 nm or less. To remove coarse particles, this dispersion was filtered under pressure using a polyvinylidene fluoride membrane filter with an average pore size of 5.0 μm to obtain a polymer-dispersed white pigment dispersion containing 50% by mass of white pigment. The pigment particles in the obtained polymer-dispersed white pigment dispersion were measured using a particle size distribution analyzer (Nanorakku UPA-EX150, manufactured by Nikkiso Co., Ltd.). The cumulative 50% volume particle diameter D 50 was 283 nm.

[0148] <Example of resin particle synthesis> -Synthesis Example 1: Synthesis of Water-Dispersible Polyurethane Resin A- In a reaction vessel equipped with a thermometer, a nitrogen gas inlet tube, and a stirrer, 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, and 0.5 parts by mass of dibutyltin oxide were charged while introducing nitrogen gas, and a polycondensation reaction was carried out at 230°C for 15 hours at 180°C to 230°C until the acid value reached 1 mgKOH / g or less, yielding polyester polyol P-1 having a hydroxyl value of 74.5 mgKOH / g, an acid value of 0.2 mgKOH / g, and an average molecular weight of 1,500. 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 into a reaction vessel equipped with a thermometer, a nitrogen gas inlet tube, and a stirrer while introducing nitrogen gas, and a polycondensation reaction was carried out at 230°C for 15 hours at 180°C to 230°C until the acid value reached 1 mgKOH / g or less, thereby obtaining polyester polyol Q-1 having an aromatic cyclic structure with a hydroxyl value of 190 mgKOH / g and an acid value of 0.3 mgKOH / g. Next, 1,000 parts by weight of the resulting polyester polyol P-1 was dehydrated at 100°C under reduced pressure. After cooling to 80°C, 907 parts by weight of methyl ethyl ketone was added, thoroughly stirred, and dissolved. 80 parts by weight of 2,2'-dimethylolpropionic acid was added. 281 parts by weight of isophorone diisocyanate was then added and reacted at 75°C for 8 hours to carry out the urethane-forming step. After confirming that the isocyanate value was 0.1% by weight or less, the mixture was cooled to 50°C, and 340 parts by weight of the resulting polyester polyol Q-1 was added to form a homogeneous solution. 60 parts by weight of triethylamine was added for neutralization, and 7,000 parts by weight of water was added to dissolve the solution in water. The resulting transparent reaction product was heated under reduced pressure at 40°C to 60°C to remove methyl ethyl ketone. Water was then added to adjust the concentration, yielding an aqueous dispersion containing a stable, translucent, colloidal water-dispersible polyurethane resin A with a nonvolatile content of 30% by weight. The water-dispersible polyurethane resin A has a structure represented by the above structural formula (A).

[0149] -Synthesis Example 2: Synthesis of Water-Dispersible Polyurethane Resin B- 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, and then cooled to 80°C. 907 parts by mass of methyl ethyl ketone was added, and the mixture was 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 carry out 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-soluble by adding 7,000 parts by mass of water. The resulting transparent reaction product was heated under reduced pressure at 40°C to 60°C to remove methyl ethyl ketone, and water was then added to adjust the concentration, yielding an aqueous dispersion containing a stable, translucent, colloidal water-dispersible polyurethane resin B with a nonvolatile content of 30%. The water-dispersible polyurethane resin B has the structure represented by structural formula (A) above.

[0150] -Synthesis Example 3: Synthesis of Water-Dispersible Polyurethane Resin C- A thermometer, a nitrogen gas inlet tube, and a reaction vessel equipped with a stirrer were charged with 664 parts by weight of terephthalic acid, 631 parts by weight of isophthalic acid, 472 parts by weight of 1,4-butanediol, 447 parts by weight of neopentyl glycol, and 0.5 parts by weight of dibutyltin oxide while introducing nitrogen gas. After esterification at 180 ° C to 230 ° C for 5 hours, the mixture was subjected to a polycondensation reaction at 230 ° C for 6 hours until the acid value reached 1 mg KOH / g or less. Next, the mixture was cooled to 120 ° C, and 321 parts by weight of adipic acid and 268 parts by weight of 2,2'-dimethylolpropionic acid were added. The mixture was then heated again to 170 ° C and reacted at this temperature for 20 hours to obtain a polyester polyol P-2 containing carboxyl groups with an acid value of 46.5 mg KOH / g and a hydroxyl value of 59.8 mg KOH / g. 1,000 parts by weight of the resulting polyester polyol P-2 was dehydrated at 100°C under reduced pressure, then cooled to 80°C. 812 parts by weight of methyl ethyl ketone was added, thoroughly stirred, and dissolved. 20 parts by weight of 1,4-butanediol was added. Next, 198 parts by weight of dicyclohexylmethane-4,4'-diisocyanate (hydrogenated MDI) was added and the mixture was allowed to react at 75°C for 8 hours. After confirming that the isocyanate content was 0.1% by weight or less, the mixture was cooled to 50°C, neutralized with 84 parts by weight of triethylamine, and then water was added to dissolve the mixture in water. The resulting transparent reaction product was heated to 40°C to 60°C under reduced pressure to remove methyl ethyl ketone. Water was then added to adjust the concentration, yielding an aqueous dispersion containing a stable, translucent, colloidal water-dispersible polyurethane resin C with a nonvolatile content of 30%. The water-dispersible polyurethane resin C has the structure shown in structural formula (A) above.

[0151] -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, and then cooled to 80°C. 907 parts by mass of methyl ethyl ketone was added, and the mixture was 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 carry out 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 was added to solubilize it. The resulting transparent reaction product was heated to 40°C to 60°C under reduced pressure to remove methyl ethyl ketone, and water was then added to adjust the concentration, yielding an aqueous dispersion containing a stable, translucent, colloidal water-dispersible polyurethane resin D with a nonvolatile content of 30% by mass. The water-dispersible polyurethane resin D has the structure represented by structural formula (A) above.

[0152] -Synthesis Example 5: Synthesis of acrylic-silicone resin- After thoroughly replacing the atmosphere in a 1-L flask equipped with a mechanical stirrer, thermometer, nitrogen gas inlet tube, reflux tube, and dropping funnel with nitrogen, 8.0 g of Latemul S-180 (Kao Corporation, reactive anionic surfactant) was added to 350 g of ion-exchanged water and mixed, and the temperature was raised to 65 ° C. Next, 3.0 g of reaction initiator t-butyl peroxobenzoate and 1.0 g of sodium isoascorbate were added, and after 5 minutes, a mixture of 45 g of methyl methacrylate, 160 g of 2-ethylhexyl methacrylate, 5 g of acrylic acid, 45 g of butyl methacrylate, 30 g of cyclohexyl methacrylate, 15 g of vinyltriethoxysilane, 8.0 g of Latemul S-180, and 340 g of ion-exchanged water was added dropwise over 3 hours. Next, the mixture was heated and aged at 80 ° C for 2 hours, cooled to room temperature, and the pH was adjusted to 7-8 with sodium hydroxide. Next, the ethanol was distilled off using 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. 50 When measured using a particle size distribution analyzer (Nanotrac UPA-EX150, manufactured by Nikkiso Co., Ltd.), the particle size was 125 nm.

[0153] <Examples of manufacturing white ink and color ink> -Production Example 1: Production of Ink 1- A vessel equipped with a stirrer was charged with 1.00 parts by weight of 2-ethyl-1,3-hexanediol, 22.00 parts by weight of glycerin, 11.00 parts by weight of 1,3-butanediol, 0.320 parts by weight of 2,5,8,11-tetramethyldecane-5,8-diol, and 0.08 parts by weight of Unidyne DSN403N, and mixed and stirred for 30 minutes. Next, 0.05 parts by weight of an antiseptic and antifungal agent (Avecia, Proxel GXL), 0.30 parts by weight of 2-amino-2-ethyl-1,3-propanediol, 40.00 parts by weight of the magenta pigment-containing polymer microparticle dispersion of Preparation Example 5, 20.00 parts by weight of the aqueous dispersion of Water-Dispersible Polyurethane Resin A of Synthesis Example 1, and a total amount of high-purity water to make 100 parts by weight were added, and mixed and stirred for 60 minutes. The resulting mixture was then pressure filtered through a polyvinylidene fluoride membrane filter with an average pore size of 1.2 μm to remove coarse particles and dust, thereby obtaining ink 1.

[0154] -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 ink formulation 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 content is expressed as the total amount, not as the amount of solids (or amount of active ingredient).

[0155] The details of the various materials shown in Tables 1 to 9 are as follows: --Colorant-- AC-RW7: White pigment dispersion, manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd., pigment solid content 45.3% by mass --resin-- Superflex 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, Inc. --Surfactants-- TEGO Wet270: Polyether-modified siloxane compound, manufactured by Evonik, 100% active ingredient Silface SAG503A: Polyether-modified siloxane compound, manufactured by Nissin Chemical Industry Co., Ltd., 100% active ingredient Surfynol 104E: Manufactured by Nissin Chemical Industry Co., Ltd., active ingredient 50% Unidyne DSN403N: Polyoxyethylene perfluoroalkyl ether, manufactured by Daikin Industries, Ltd., 100% active ingredient --Mold inhibitor-- Proxel GXL: Antifungal agent containing 1,2-benzisothiazolin-3-one as its main ingredient (manufactured by Avecia, 20% active ingredient, contains dipropylene glycol)

[0156] [Table 1]

[0157] [Table 2]

[0158] [Table 3]

[0159] [Table 4]

[0160] [Table 5]

[0161] [Table 6]

[0162] [Table 7]

[0163] [Table 8]

[0164] [Table 9]

[0165] <Physical properties of white ink and color ink> Next, various physical properties were measured as follows for the resulting inks 1 to 45. The results are shown in Table 10.

[0166] -viscosity- The viscosity of the ink was measured at 25°C using a viscometer (RE-85L, manufactured by Toki Sangyo Co., Ltd.).

[0167] -pH- The pH of the ink was measured at 25°C using a pH meter (HM-30R model, manufactured by TOA-DKK Corporation).

[0168] -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.).

[0169] -Dynamic surface tension- The dynamic surface tension of the ink was measured at 25° C. using a SITA DynoTester (manufactured by SITA) when the bubble lifetime was 15 msec, 150 msec, and 1500 msec by the maximum bubble pressure method.

[0170] [Table 10]

[0171] <Pretreatment liquid manufacturing example> -Production Example 1: Production of Pretreatment Solution 1- 7.5 parts by weight of ammonium lactate was weighed into a glass beaker, and 50.00 parts by weight of high-purity water was added and stirred for 5 minutes. Next, 10.00 parts by weight of propylene glycol, 0.1 parts by weight of Olfine EXP.4300, 0.05 parts by weight of Proxel GXL, and 0.1 parts by weight of 1,2,3-benzotriazole were added and mixed and stirred for 15 minutes. Further, high-purity water was added to make a total of 100 parts by weight, and mixed and stirred for 10 minutes. This mixture was pressure-filtered through a polyvinylidene fluoride membrane filter with an average pore size of 5.0 μm to remove insoluble matter and other debris, producing pretreatment solution 1.

[0172] -Production Examples 2 to 16: Production of Pretreatment Solutions 2 to 16- Pretreatment solutions 2 to 16 were obtained in the same manner as in Preparation Example 1, except that the formulation of the pretreatment solution 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 content is expressed as the total amount, not as the amount of solids (or amount of active ingredient).

[0173] The details of the various materials shown in Tables 11 to 13 are as follows: --Cationic polymer-- Sharol 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 Corporation --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-- Arrowbase CB-1200: 23% solids by mass, manufactured by Unitika Ltd. --Surfactants-- Olfin EXP.4300, manufactured by Nissin Chemical Industry Co., Ltd., active ingredient 60% by mass --wax-- AQUACER 497: Paraffin wax, active ingredient 50% by weight, manufactured by BYK Japan Co., Ltd. AQUACER539: Modified paraffin wax, active ingredient 35% by weight, manufactured by BYK Japan Co., Ltd. AQUACER531: Modified polyethylene wax, active ingredient 45% by weight, manufactured by BYK Japan Co., Ltd. --Mold inhibitor-- Proxel GXL: Antifungal agent containing 1,2-benzisothiazolin-3-one as its main ingredient (manufactured by Avecia, 20% active ingredient, contains dipropylene glycol)

[0174] <Storage stability of pretreatment solution> The resulting pretreatment solutions 1 to 16 were then stored for 10 days in a heated environment at 60°C, and changes in the pretreatment solutions during storage were evaluated according to the following evaluation criteria. The results are shown in Tables 11 to 13. (Evaluation criteria) A: No noticeable changes B: Coagulation or thickening occurs, making it difficult to use as a pretreatment liquid

[0175] [Table 11]

[0176] [Table 12]

[0177] [Table 13]

[0178] <Image formation using ink set> (Examples 1 to 18, Comparative Examples 1 to 7) Under environmental conditions adjusted to 23°C ± 0.5°C and 50% ± 5% RH, an inkjet printing device (Direct to Garment Printer RICOH Ri 6000, manufactured by Ricoh Co., Ltd.) was used, and the driving voltage of the piezoelectric element was varied to ensure a uniform amount of ink was ejected, so that the same amount of ink was deposited on the recording medium. First, a predetermined pretreatment liquid was applied to a predetermined recording medium in a predetermined amount by a predetermined application method, as shown in Table 14. Thereafter, if the recording medium was coated paper, PVC film, or PET film, it was dried in an oven at 70°C for 120 seconds, if it was a dark-colored polyester T-shirt, it was dried in an oven at 130°C for 90 seconds, and if it was a dark-colored cotton T-shirt, it was dried in an oven at 165°C for 90 seconds. Next, the inkjet printing device was filled with the white ink and color inks contained in the predetermined ink sets shown in Table 14, and a solid image was formed by applying the white ink in the predetermined application amounts shown in Table 14 to the areas of the recording medium to which the pretreatment liquid had been applied. 17 seconds after the application of the white ink, the color inks were applied in the predetermined application amounts shown in Table 14 to the areas of the recording medium to which the white ink had been applied, to form the chart shown in Figure 3. The recording medium was not heated between the application of the white ink and the application of the color inks. Next, the recording medium on which the chart shown in Figure 3 was formed was dried in an oven at 70°C for 5 minutes if the recording medium was coated paper, PVC film, or PET film, dried in an oven at 130°C for 3 minutes if the recording medium was a dark-colored polyester T-shirt, or dried in an oven at 165°C for 2 minutes if the recording medium was a dark-colored cotton T-shirt, thereby obtaining a sample image. In Figure 3, W represents a white solid image area as a base, Y represents a yellow solid image area formed on the base W, M represents a magenta solid image area formed on the base W, C represents a cyan solid image area formed on the base W, R represents a red solid image area formed on the base W, B represents a blue solid image area formed on the base W, G represents a green solid image area formed on the base W, K represents a black solid image area formed on the base W, k1 to k6 represent the black letter "R" formed on the base W, and y represents the yellow letter "R" formed on the base W. The chart shown in Figure 3 was created from an image digitized without color correction using Adobe Photoshop software and printed at 600 dpi x 600 dpi.

[0179] The details of the 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 material thickness 120 μm / adhesive thickness 25 μm, manufactured by Nichie Co., Ltd. Lumirror #50-T11: Transparent PET film, easy-adhesion treatment, manufactured by Toray Industries, Inc. 00300-ACT: Dark polyester T-shirt, Glimmer 00300-ACT Black, manufactured by TMS Co., Ltd. 00085-CVT: Dark cotton T-shirt, Printstar 00085-CVT Black, manufactured by TOM'S Co., Ltd.

[0180] [Table 14]

[0181] Each sample image was evaluated for Hunter brightness, color bleeding, and beading as follows, and the results are shown in Table 15.

[0182] [Hunter Whiteness] The image density of 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 using the following calculation formula (1), and evaluated based on the following evaluation criteria. The image density was measured by placing the sample image on five sheets of medium-weight black color wood-free paper (manufactured by Hokuetsu Corporation) stacked together. However, in Examples 1 to 3, the recording media used were originally white, and there was no point in measuring the Hunter whiteness, so they were not evaluated. (Evaluation criteria) A+: Hunter whiteness is 85 or higher 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 whiteness is less than 70

[0183]

number

[0184] [Color Bleed] In the solid image areas of each color of the obtained sample images, the degree of color bleeding between adjacent white solid image areas (e.g., bleeding at the color boundary between white and yellow) and between adjacent solid image areas of other colors (e.g., bleeding at the color boundary between black and yellow) was visually observed and evaluated based on the following evaluation criteria. (Evaluation criteria) A+: No bleeding occurs on the color boundary A: Very slight bleeding occurs at the color boundary. B: Slight bleeding occurs at the color boundary C: Bleeding occurs at the color boundary D: Significant bleeding occurs at the color boundary.

[0185] [Beading] The degree of beading (uneven density) 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 uneven density B: Slight density unevenness C: Uneven density occurs D: Significant density unevenness

[0186] [Table 15] [Explanation of symbols]

[0187] 400 Image forming device 401 Exterior of image forming device 401c Device body cover 404 Cartridge Holder 410p Pretreatment liquid containing means 410w white ink container 410k black ink container 410c Cyan ink containing means 411 Storage Unit 413 Outlet 414 Storage container case 420 Mechanism Department 434 Inkjet ejection head 436 Supply Tube [Prior art documents] [Patent documents]

[0188] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-266853

Claims

1. 1. An image forming method comprising: a white ink applying step of applying a white ink to a recording medium; and a color ink applying step of applying a color ink to an area of ​​the recording medium to which the white ink has been applied, a difference in static surface tension between the white ink and the color ink at 25° C. is 1.0 mN / m or less; a difference in dynamic surface tension at 25° C. when a bubble lifetime is 15 msec, 150 msec, and 1500 msec, as determined by a maximum bubble pressure method, between the white ink and the color ink is independently 1.0 mN / m or less; an image forming method that does not include a heating step of heating the recording medium to which the white ink has been applied between the white ink applying step and the color ink applying step;

2. 2. The image forming method according to claim 1, further comprising a pretreatment liquid application step of applying a pretreatment liquid to an area of ​​the recording medium onto which the white ink is to be applied, prior to the white ink application step.

3. 3. The image forming method according to claim 1, wherein the time from when the white ink is applied to the recording medium until when the color ink is applied to the area of ​​the recording medium to which the white ink has been applied is within 20 seconds.

4. 4. The image forming method according to claim 1, wherein the recording medium is a dark-colored fabric.

Images