Ink set and recording method

Abstract

To provide a treatment liquid and dark ink composition and light ink composition-including ink set that can yield excellent image quality and excellently reduce deviation of landing position.SOLUTION: The ink set according to the present invention includes a treatment liquid containing a coagulant, and a dark ink composition and a light ink composition that contain a coloring material, are of the same color system, and are water-based inkjet ink, and in which the light ink composition contains an organic solvent that is a condensate of an alkanediol having 2 or 3 carbon atoms and has two hydroxyl groups, and the dark ink composition contains an organic solvent that is an alkanediol having 2 to 4 carbon atoms.SELECTED DRAWING: None

Description

Technical Field

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

Background Art

[0002] An inkjet recording method is known in which minute ink droplets are ejected from nozzles of a discharge head of an inkjet recording apparatus to record an image on a recording medium. In recent years, for example, it has been used not only for recording an image on a recording medium having excellent ink absorbency such as plain paper, but also for recording an image on a low-absorbency recording medium having low ink absorbency such as art paper or coated paper, or a non-absorbency recording medium that hardly absorbs ink such as a plastic film. And, for recording an image on such a low-absorbency recording medium or non-absorbency recording medium, water-based inkjet ink (hereinafter, also referred to as "aqueous ink") has also come to be used.

[0003] In recording using aqueous ink, in order to prevent ink droplets from gathering and bleeding on the recording medium and deteriorating the image quality, there is a technique of using a treatment liquid that aggregates the components of the ink in combination with the aqueous ink. And, in recent years, as the aqueous ink used together with the treatment liquid, there is a technique of obtaining an image having high gradation by using a combination of a dark ink and a light ink that are of the same color system but different in color density (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, even when using a treatment liquid, the image quality of light ink was not sufficient. Also, while improving the image quality of light ink, it was difficult to match the ejection characteristics of light ink and dark ink. When ejecting dark ink and light ink (hereinafter also referred to as "dark and light ink") simultaneously, there was a problem that the landing positions of dark and light ink droplets shifted. That is, conventionally, it has not been possible to obtain excellent image quality while using a treatment liquid, dark ink, and light ink, and excellently reducing the shift in the landing positions of dark and light ink droplets (landing shift).

Means for Solving the Problems

[0006] One aspect of the ink set according to the present invention is a treatment liquid containing a flocculant, a dark ink composition and a light ink composition, which contain coloring materials, are of the same color system, and are aqueous inkjet inks, the light ink composition contains an organic solvent that is a condensate of an alkanediol having 2 or 3 carbon atoms and has 2 hydroxyl groups, the dark ink composition contains an organic solvent that is an alkanediol having 2 to 4 carbon atoms.

[0007] One aspect of the recording method according to the present invention is a recording method using the ink set of the above aspect, including a step of attaching the treatment liquid to a recording medium, and a step of attaching the light ink composition and the dark ink composition to the recording medium by an inkjet method.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Mode for Carrying Out the Invention

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

[0010] 1. Ink set An ink set according to an embodiment of the present invention comprises a treatment liquid containing a flocculant, a concentrated ink composition and a light ink composition, which contain a coloring material, are of the same color system, and are water-based inkjet inks. The light ink composition contains an organic solvent which is a condensate of an alkanediol having 2 or 3 carbon atoms and has 2 hydroxyl groups. The concentrated ink composition contains an organic solvent which is an alkanediol having 2 to 4 carbon atoms.

[0011] According to the ink set of this embodiment, excellent image quality can be obtained, and landing deviation can be excellently reduced.

[0012] Since the light ink generally has a lower content of the coloring material, which is an aggregating component, compared to the concentrated ink, its reactivity with the treatment liquid is lower than that of the concentrated ink, and the resulting image quality is likely to be insufficient. Also, even if the image quality of the light ink could be improved, it was difficult to match the ejection characteristics of the light ink and the concentrated ink, and there was a problem that landing deviation occurred when both were ejected simultaneously. In this case, by adding to the light ink composition an organic solvent which is a condensate of an alkanediol having 2 or 3 carbon atoms and has two hydroxyl groups (hereinafter also referred to as "specific condensate"), excellent image quality was obtained. It is presumed that this is because, by containing a specific condensate having a relatively high viscosity, when the drying of the light ink composition proceeds on the recording medium, the ink greatly thickens, and thus the movement of the ink droplets is more suppressed. That is, it is presumed that due to the fixing effect (pinning effect) of the ink droplets on the recording medium by the reaction with the treatment liquid and the pinning effect due to the thickening of the ink droplets themselves, the ink droplets can be fixed before they gather and bleed, and thus excellent image quality was obtained. Furthermore, by adding to the dark ink composition an organic solvent which is an alkanediol having 2 to 4 carbon atoms (hereinafter also referred to as "specific monomer"), the ejection characteristics of the dark ink composition and the light ink composition can be matched, and it has become possible to excellently reduce the landing deviation. It is presumed that this is because the specific condensate contained in the light ink composition and the specific monomer contained in the dark ink composition are similar compounds, and therefore, their ejection characteristics (particularly, viscosity) have also become similar. Also, when the content of the coloring material contained in the ink is small, the viscosity tends to be low, but it is also presumed that this is because when the light ink composition contains a specific condensate, the viscosity becomes appropriate and the ejection characteristics are easily matched.

[0013] In the present invention, "ink set" refers to a dark ink composition, a light ink composition, and a treatment liquid that are used for recording as a set. That is, it refers to a dark ink composition, a light ink composition, and a treatment liquid that perform recording using both the dark ink composition and the light ink composition and the treatment liquid. The dark ink composition, the light ink composition, and the treatment liquid included in the ink set may each be accommodated in a separate liquid container, or may be accommodated in an integrated liquid container.

[0014] The ink set includes at least one (type) of dark ink composition, at least one (type) of light ink composition, and at least one (type) of treatment liquid. The dark ink composition, the light ink composition, and the treatment liquid may each be provided in two or more. Note that the dark ink composition and the light ink composition are water-based inkjet inks, which are ejected from an inkjet head by an inkjet method and used for recording.

[0015] Hereinafter, the light ink composition, the dark ink composition, and the treatment liquid included in the ink set according to the present embodiment will be described.

[0016] 1.1 Light Ink Composition and Dark Ink Composition The light ink composition and the dark ink composition included in the ink set according to the present embodiment contain colorants, are of the same color system, and are water-based inkjet inks. The light ink composition contains an organic solvent that is a condensate of an alkanediol having 2 or 3 carbon atoms and has 2 hydroxyl groups, and the dark ink composition contains an organic solvent that is an alkanediol having 2 to 4 carbon atoms.

[0017] It is preferable that the content of the colorant in the light ink composition is less on a mass basis than the content of the colorant in the dark ink composition. That is, it is preferable that the ink with a higher content of the colorant on a mass basis is used as the dark ink composition, and the ink with a lower content of the colorant on a mass basis than the dark ink composition is used as the light ink composition.

[0018] That the light ink composition and the dark ink composition are "of the same color system" means, in one aspect, that both have a similar hue angle, and it means that the difference in the hue angle ∠H° of each recorded image recorded on a white recording medium using the light ink composition and the dark ink composition is within 30°. The hue angle ∠H° is defined in the CIELAB color space, and ∠H° = tan -1 (b * / a * ) + 180 (when a * < 0), or ∠H° = tan -1 (b * / a *) + 360(a * is obtained by (>0). The difference in hue angle ∠H° is preferably within 20°, more preferably within 10°.

[0019] a * and b * represent the perceptual chromaticity index defined in the CIELAB color space. The light ink composition and the dark ink composition being "the same color system" means that they are in the same color system or inks that suggest being in the same color system. For example, combinations such as cyan ink and light cyan ink (also called photo cyan ink), magenta ink and light magenta ink (also called photo magenta ink), yellow ink and light yellow ink, etc. can be mentioned. Combinations of gray ink and black ink can also be mentioned. Thus, it is a combination of inks of the same color with different shades of color. In addition, light ink compositions and dark ink compositions that contain only the same colorant with different contents from each other can be regarded as inks of the same color system.

[0020] Hereinafter, each component contained in the light ink composition and the dark ink composition included in the ink set according to the present embodiment will be described. Note that the light ink composition or the dark ink composition may also be referred to as "ink composition".

[0021] 1.1.1 Water The light ink composition and the dark ink composition included in the ink set according to the present embodiment are water-based inkjet inks and contain water. Here, the "water-based" of the "water-based" inkjet ink in the present invention means that at least water is used as the main solvent. The content of the organic solvent in the "water-based" composition is preferably 40% by mass or less, preferably 30% by mass or less, more preferably 25% by mass or less, and particularly preferably 20% by mass or less with respect to the total mass (100% by mass) of the composition. The content of water in the composition is preferably 45% by mass or more, preferably 50% by mass or more, more preferably 60% by mass or more, and particularly preferably 70% by mass or more with respect to the total mass of the composition.

[0022] Although the water is not particularly limited, examples thereof include pure water such as ion-exchanged water, ultrafiltration water, reverse osmosis permeated water, and distilled water, and those with extremely low ionic impurities such as ultrapure water. In addition, when using water sterilized by ultraviolet irradiation or addition of hydrogen peroxide, etc., generation of mold and bacteria can be prevented when the ink composition is stored for a long time. Thereby, the storage stability tends to be further improved.

[0023] 1.1.2 Colorant The light ink composition and the dark ink composition included in the ink set according to this embodiment contain a colorant.

[0024] As the colorant, either a dye or a pigment can be used, but a pigment having a property of being less likely to fade against light, gas, etc. is preferably used. An image formed on a recording medium using a pigment not only has excellent image quality but also is excellent in water resistance, gas resistance, light resistance, etc., and has good storage properties. This property is particularly remarkable when formed on a non-absorbent or low-absorbent recording medium. In this embodiment, the light ink composition and the dark ink composition may each contain the same colorant or different colorants.

[0025] <Pigment> Examples of the pigment include organic pigments such as cyan, magenta, yellow, and black, and special pigments such as white pigments and iridescent pigments.

[0026] Examples of organic pigments include quinacridone pigments, quinacridone quinone pigments, dioxane pigments, dioxazine pigments, phthalocyanine pigments, anthrapyrimidine pigments, ansanthrone pigments, indanthrone pigments, flavanthrone pigments, perylene pigments, diketopyrrolopyrrole pigments, perinone pigments, quinophthalone pigments, anthraquinone pigments, thioindigo pigments, benzimidazolone pigments, thioindigo pigments, isoindolinone pigments, azomethine pigments, dye chelates, dyed lakes, nitro pigments, nitroso pigments, aniline black, and azo pigments such as insoluble azo pigments, condensed azo pigments, azo lakes, and chelate azo pigments, etc.

[0027] Specific examples of the organic pigments include the following. Examples of cyan pigments include C.I. Pigment Blue 1, 2, 3, 15:3, 15:4, 16, 22, 60, etc.; C.I. Vat Blue 4, 60, etc., and preferably, it is a single or a mixture of two or more selected from the group consisting of C.I. Pigment Blue 15:3, 15:4, and 60.

[0028] Examples of magenta pigments include C.I. Pigment Red 5, 7, 12, 48(Ca), 48(Mn), 57(Ca), 57:1, 112, 122, 123, 168, 184, 202, C.I. Pigment Violet 19, etc., and preferably, it is a single or a mixture of two or more selected from the group consisting of C.I. Pigment Red 122, 202, and 209, C.I. Pigment Violet 19.

[0029] Examples of yellow pigments include C.I. Pigment Yellow 1, 2, 3, 12, 13, 14C, 16, 17, 73, 74, 75, 83, 93, 95, 97, 98, 119, 110, 114, 128, 129, 138, 150, 151, 154, 155, 180, 185, etc., and preferably, it is a single or a mixture of two or more selected from the group consisting of C.I. Pigment Yellow 74, 109, 110, 128, 138, 150, and 180.

[0030] As the orange pigment, it is C.I. Pigment Orange 36 or 43 or a mixture thereof.

[0031] As the green pigment, it is C.I. Pigment Green 7 or 36 or a mixture thereof.

[0032] As the black pigment, there are furnace black, lamp black, acetylene black, channel black, etc. (C.I. Pigment Black 7). As commercial products, there are No.2300, 900, MCF88, No.20B, No.33, No.40, No.45, No.52, MA7, MA8, MA100, No2200B, etc. (trade names, manufactured by Mitsubishi Chemical Corporation), Color Black FW1, FW2, FW2V, FW18, FW200, S150, S160, S170, Printex 35, U, V, 140U, Special Black 6, 5, 4A, 4, 250, etc. (trade names, manufactured by Degussa), Conductex SC, Raven 1255, 5750, 5250, 5000, 3500, 1255, 700, etc. (all of the above are trade names, manufactured by Columbian Carbon), Regal 400R, 330R, 660R, Mogul L, Monarch 700, 800, 880, 900, 1000, 1100, 1300, 1400, Elftex 12, etc. (trade names, manufactured by Cabot). These carbon blacks may be used alone or as a mixture of two or more kinds.

[0033] The glitter pigment is not particularly limited as long as it can exhibit glitter when attached to a medium. For example, it includes metal particles of one or more alloys (also referred to as metal pigments) selected from the group consisting of aluminum, silver, gold, platinum, nickel, chromium, tin, zinc, indium, titanium, and copper, and pearl pigments having a pearl luster. Representative examples of pearl pigments include pigments having a true pearl luster or an interference luster such as titanium dioxide-coated mica, fish scale foil, and bismuth oxychloride. Further, the glitter pigment may be subjected to a surface treatment for suppressing the reaction with water.

[0034] In addition, examples of the white pigment include metal oxides, metal compounds such as barium sulfate and calcium carbonate. Examples of the metal oxide include titanium dioxide, zinc oxide, silica, alumina, magnesium oxide and the like. Further, particles having a hollow structure may be used as the white pigment.

[0035] The above pigments may be used alone or in combination of two or more. From the viewpoint of storage stability such as light resistance, weather resistance, and gas resistance, the pigment is preferably an organic pigment.

[0036] [Pigment dispersion] The above pigments preferably exist in a dispersed state in the ink composition, that is, as a pigment dispersion. Here, the pigment dispersion in this specification means including a pigment dispersion liquid and a slurry of a pigment (low-viscosity aqueous dispersion).

[0037] Examples of the pigment dispersion include, but are not limited to, self-dispersible pigments, polymer-dispersed pigments, pigments coated with polymers, and the like.

[0038] (Self-dispersible pigment) A self-dispersible pigment is a pigment that can be dispersed or dissolved in an aqueous medium without a dispersant. Here, "dispersed or dissolved in an aqueous medium without a dispersant" means a state in which the pigment is stably present in the aqueous medium due to the hydrophilic groups on its surface without using a dispersant for dispersing the pigment. Therefore, there is almost no foaming due to a decrease in defoaming property caused by the dispersant, and it is easy to prepare an ink with excellent ejection stability. In addition, since a significant increase in viscosity caused by the dispersant is suppressed, it is possible to contain more pigments and sufficiently increase the printing density, and thus it is easy to handle.

[0039] The above hydrophilic groups are preferably one or more hydrophilic groups selected from the group consisting of -OM, -COOM, -CO-, -SO3M, -SO2M, -SO2NH2, -RSO2M, -PO3HM, -PO3M2, -SO2NHCOR, -NH3, and -NR3.

[0040] In these chemical formulas, M represents a hydrogen atom, an alkali metal, ammonium, a phenyl group which may have a substituent, or an organic ammonium, and R represents an alkyl group having 1 to 12 carbon atoms or a naphthyl group which may have a substituent. Further, the above M and R are each independently selected.

[0041] The self-dispersible pigment is produced, for example, by subjecting the pigment to a physical treatment or a chemical treatment to bond (graft) the hydrophilic group to the surface of the pigment. Examples of the physical treatment include vacuum plasma treatment and the like. Examples of the chemical treatment include a wet oxidation method of oxidizing with an oxidizing agent in water, a method of bonding a carboxyl group via a phenyl group by bonding p-aminobenzoic acid to the pigment surface, and the like.

[0042] (Polymer-dispersed pigment) The polymer-dispersed pigment is a pigment that can be dispersed by polymer dispersion. The polymer used for the polymer-dispersed pigment is not limited to the following, but for example, the glass transition temperature (Tg) of the dispersion polymer used for pigment dispersion is preferably 80°C or lower, more preferably 70°C or lower. When the Tg is 80°C or lower, the fixing property of the ink may be improved.

[0043] Further, the weight average molecular weight of the above polymer by gel permeation chromatography (GPC) is preferably 10,000 or more and 200,000 or less. Thereby, the storage stability of the ink may be further improved. Here, the weight average molecular weight (Mw) in this specification can be measured as the weight average molecular weight in terms of polystyrene using gel permeation chromatography (GPC) of the L7100 system manufactured by Hitachi, Ltd.

[0044] As the polymer, since it tends to be further excellent in ink fixing property and glossiness, it is preferable that 70 mass% or more of its constituent components is a polymer obtained by copolymerization of (meth)acrylate and (meth)acrylic acid. It is preferable that it is polymerized from a monomer component in which at least one of an alkyl (meth)acrylate having 1 to 24 carbon atoms and a cyclic alkyl (meth)acrylate having 3 to 24 carbon atoms is 70 mass% or more. Specific examples of the monomer component include, but are not limited to, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, t-butylcyclohexyl (meth)acrylate, lauryl (meth)acrylate, isobornyl (meth)acrylate, cetyl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, tetramethylpiperidyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyl oxy (meth)acrylate, and behenyl (meth)acrylate. Further, as other monomer components for polymerization, hydroxy (meth)acrylates having a hydroxyl group such as hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, and diethylene glycol (meth)acrylate, urethane (meth)acrylate, and epoxy (meth)acrylate can also be used.

[0045] In the present specification, the notation with (meth)acryl means at least one of acrylic and methacrylic. The notation with (meth)acrylate means at least one of acrylate and methacrylate.

[0046] (Pigment coated with polymer) In addition, since it tends to be excellent in ink fixability, glossiness, and color reproducibility, among the above polymer-dispersed pigments, pigments coated with a polymer, that is, microencapsulated pigments, are preferably used.

[0047] The pigment coated with the polymer is obtained by the phase inversion emulsification method. That is, the above polymer is dissolved in an organic solvent such as methanol, ethanol, isopropanol, n-butanol, acetone, methyl ethyl ketone, and dibutyl ether. A pigment is added to the obtained solution, and then a neutralizing agent and water are added and kneaded and dispersed to prepare an oil-in-water type dispersion. Then, by removing the organic solvent from the obtained dispersion, a pigment coated with a polymer can be obtained as an aqueous dispersion. For the kneading and dispersion treatment, for example, a ball mill, a roll mill, a bead mill, a high-pressure homogenizer, and a high-speed stirring type disperser can be used.

[0048] As the neutralizing agent, tertiary amines such as ethylamine and trimethylamine, lithium hydroxide, sodium hydroxide, potassium hydroxide, and ammonia are preferable. The pH of the obtained aqueous dispersion is preferably 6 to 10.

[0049] As the polymer for coating the pigment, those having a weight average molecular weight of about 10,000 to 150,000 by GPC are preferable in terms of stably dispersing the pigment.

[0050] <Dye> For the light ink composition and the dark ink composition, a dye may be used as the coloring material. The dye is not particularly limited, and acid dyes, direct dyes, reactive dyes, basic dyes, and disperse dyes can be used. Examples of the dye include C.I. Acid Yellow 17, 23, 42, 44, 79, 142, C.I. Acid Red 52, 80, 82, 249, 254, 289, C.I. Acid Blue 9, 45, 249, C.I. Acid Black 1, 2, 24, 94, C.I. Food Black 1, 2, C.I. Direct Yellow 1, 12, 24, 33, 50, 55, 58, 86, 132, 142, 144, 173, C.I. Direct Red 1, 4, 9, 80, 81, 132, 225, 227, C.I. Direct Blue 1, 2, 15, 71, 86, 87, 98, 165, 199, 202, C.I. Direct Black 19, 38, 51, 71, 154, 168, 171, 195, C.I. Reactive Red 14, 32, 55, 79, 141, 249, C.I. Reactive Black 3, 4, 35.

[0051] The coloring material may be used alone or in combination of two or more.

[0052] The content of the coloring material in the light ink composition is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, still more preferably 0.5% by mass or more, and particularly preferably 0.7% by mass or more with respect to the total mass of the light ink composition. Also, the content of the coloring material in the light ink composition is preferably 10% by mass or less, more preferably 5% by mass or less, still more preferably 3% by mass or less, particularly preferably 2% by mass or less, and even more particularly preferably 1.5% by mass or less with respect to the total mass of the light ink composition.

[0053] The content of the coloring material in the concentrated ink composition is preferably 0.5% by mass or more, more preferably 1% by mass or more, still more preferably 2% by mass or more, and particularly preferably 3% by mass or more with respect to the total mass of the concentrated ink composition. Further, the content of the coloring material in the concentrated ink composition is preferably 15% by mass or less, more preferably 10% by mass or less, still more preferably 7% by mass or less, and particularly preferably 5% by mass or less with respect to the total mass of the concentrated ink composition.

[0054] As described above, the content of the coloring material in the light ink composition is preferably less than that in the concentrated ink composition on a mass basis. The content of the coloring material in the light ink composition is preferably 0.5% by mass or more less than that in the concentrated ink composition on a mass basis, more preferably 1 to 6% by mass less, and still more preferably 2 to 5% by mass less.

[0055] 1.1.3 Organic solvent The light ink composition included in the ink set according to the present embodiment contains an organic solvent (specific condensate) having 2 hydroxyl groups, which is a condensate of an alkanediol having 2 or 3 carbon atoms, and the concentrated ink composition contains an organic solvent (specific monomer) which is an alkanediol having 2 to 4 carbon atoms.

[0056] 1.1.3.1 Specific condensate The light ink composition contains an organic solvent (specific condensate) having 2 hydroxyl groups, which is a condensate of an alkanediol having 2 or 3 carbon atoms. The specific condensate is a condensate of two or more molecules of an alkanediol having 2 or 3 carbon atoms. It is a condensate formed by the condensation of hydroxyl groups with each other between molecules.

[0057] Among specific condensates, examples of those that are condensates of alkanediols with 2 carbon atoms and have two hydroxyl groups include, for example, diethylene glycol (standard boiling point 244 °C, condensation number 2), triethylene glycol (standard boiling point 276 °C, condensation number 3), tetraethylene glycol (standard boiling point 328 °C, condensation number 4), pentaethylene glycol (standard boiling point 184 °C, condensation number 5), and the like.

[0058] Among specific condensates, examples of those that are condensates of alkanediols with 3 carbon atoms and have two hydroxyl groups include dipropylene glycol (standard boiling point 232 °C, condensation number 2), tripropylene glycol (standard boiling point 270 °C, condensation number 3), tetrapropylene glycol (condensation number 4), pentapropylene glycol (condensation number 5), and the like.

[0059] The condensation number of specific condensates is preferably 2 to 5, more preferably 2 to 3. Here, the "condensation number" refers to the number of molecules of alkanediol with 2 or 3 carbon atoms that have condensed.

[0060] The standard boiling point of specific condensates is preferably 150 to 300 °C, more preferably 150 to 250 °C. Also, the standard boiling point of specific condensates is preferably 200 to 300 °C, more preferably 210 to 250 °C. Furthermore, 200 to 240 °C is preferred.

[0061] Furthermore, the organic solvent (specific condensate) that is a condensate of alkanediol with 2 or 3 carbon atoms and has two hydroxyl groups contained in the light ink composition, and the organic solvent (specific monomer) that is the alkanediol with 2 to 4 carbon atoms contained in the concentrated ink composition described later each preferably have a standard boiling point of 150 to 300 °C, and each more preferably have a standard boiling point of 150 to 250 °C. When the standard boiling point of each is within the above range, the ink has excellent drying properties and the rubbing resistance tends to be further improved.

[0062] The content of the specific condensate in the light ink composition is preferably 0.50% by mass or more, more preferably 1.0% by mass or more, still more preferably 1.5% by mass or more, and particularly preferably 3.0% by mass or more with respect to the total mass of the light ink composition. Also, the content of the specific condensate in the light ink composition is preferably 15% by mass or less, more preferably 10% by mass or less, still more preferably 8.0% by mass or less, further preferably 6.0% by mass or less, and particularly preferably 5.0% by mass or less with respect to the total mass of the light ink composition.

[0063] The specific condensate may or may not be contained in the concentrated ink composition. However, it is preferable that the concentrated ink composition does not contain an organic solvent (specific condensate) which is a condensate of an alkanediol having 2 or 3 carbon atoms and has 2 hydroxyl groups, in an amount exceeding the content of the organic solvent (specific condensate) which is a condensate of an alkanediol having 2 or 3 carbon atoms and has 2 hydroxyl groups in the light ink composition. Furthermore, it is preferable that the concentrated ink composition does not contain the specific condensate in an amount equal to or more than the content of the specific condensate in the light ink composition. Furthermore, the content of the specific condensate in the concentrated ink composition is preferably at least 1% by mass less, and preferably at least 3% by mass less than the content of the specific condensate in the light ink composition. Also, it is preferable that the concentrated ink composition does not contain the specific condensate in an amount equal to or more than the content of the specific monomer described later in the concentrated ink composition. Furthermore, it is preferably at least 3% by mass less, preferably at least 5% by mass less, preferably at least 7% by mass less, and preferably at least 10% by mass less than the content of the specific monomer in the concentrated ink composition. Moreover, it is more preferable that the concentrated ink composition does not contain the specific condensate.

[0064] Inks containing a specific condensate tend to have improved clogging recovery properties because of the high moisture retention of the specific condensate. On the other hand, since concentrated ink compositions are often used at high duty, when a specific condensate is contained, sufficient drying property may not be ensured and the abrasion resistance may be poor. Further, when the ink contains a large amount of coloring material, landing position deviation tends to occur easily during recording. Therefore, in a concentrated ink composition, it is preferable not to use or use a small amount of a specific condensate that increases the viscosity.

[0065] In this specification, "duty" is a value calculated by the following formula (1). duty (%) = {actual printed dot number / (vertical resolution × horizontal resolution)} × 100 (1) (In the formula, "actual printed dot number" is the number of actual printed dots per unit area, and "vertical resolution" and "horizontal resolution" are the resolutions per unit area, respectively.)

[0066] In addition, the content of the specific condensate in the concentrated ink composition is preferably 4.0% by mass or less, more preferably 2.0% by mass or less, even more preferably 1.0% by mass or less, still more preferably 0.50% by mass or less, and particularly preferably 0% by mass, based on the total mass of the concentrated ink composition.

[0067] 1.1.3.2 Specific Monomer The concentrated ink composition contains an organic solvent (specific monomer) that is an alkanediol having 2 to 4 carbon atoms. Since such a specific monomer is a compound similar to the specific condensate contained in the light ink composition, the compatibility between the two is good and a uniform image tends to be obtained.

[0068] Examples of specific monomers include ethylene glycol (standard boiling point 197°C), propylene glycol (standard boiling point 188°C), 1,2-butanediol (standard boiling point 192°C), 1,3-propanediol (standard boiling point 214°C), 1,3-butanediol (standard boiling point 207°C), 1,4-butanediol (standard boiling point 235°C), 2,3-butanediol (standard boiling point 182°C), 2-methyl-1,3-propanediol (standard boiling point 214°C), and the like. Among these, it is preferable that the organic solvent is an alkanediol having 2 or 3 carbon atoms.

[0069] The standard boiling point of the specific monomer is preferably 150 to 300°C, more preferably 150 to 250°C. Also, the standard boiling point of the specific monomer is preferably 150 to 240°C, more preferably 150 to 200°C. Further, 150 to 190°C is preferable.

[0070] The content of the specific monomer in the concentrated ink composition is preferably 1.0% by mass or more, more preferably 3.0% by mass or more, still more preferably 5.0% by mass or more, and particularly preferably 8.0% by mass or more with respect to the total mass of the concentrated ink composition. Also, the content of the specific monomer in the concentrated ink composition is preferably 20% by mass or less, more preferably 18% by mass or less, still more preferably 16% by mass or less, and particularly preferably 14% by mass or less with respect to the total mass of the concentrated ink composition.

[0071] Since the concentrated ink composition contains a specific monomer, it tends to have excellent abrasion resistance. This is because the specific monomer has a lower standard boiling point compared to the organic solvents such as the above-mentioned specific condensates and is excellent in the drying property of the ink. From the viewpoint of excellent drying property, it is preferable that the specific monomer is an organic solvent which is an alkanediol having 2 to 3 carbon atoms. Also, although the specific monomer has a lower pinning effect compared to the specific condensate, the concentrated ink composition is excellent in reactivity with the treatment liquid compared to the light ink composition, so that excellent image quality can be obtained.

[0072] A specific monomer may or may not be contained in the light ink composition. However, the light ink composition preferably contains an organic solvent (specific monomer) which is an alkanediol having 2 to 4 carbon atoms. The light ink composition preferably has a content of the specific monomer higher than the content of the specific condensate. That is, in the light ink composition, the content of an organic solvent (specific condensate) which is a condensate of an alkanediol having 2 or 3 carbon atoms and has two hydroxyl groups is preferably less than the content of an organic solvent (specific monomer) which is an alkanediol having 2 to 4 carbon atoms. Furthermore, the light ink composition preferably has the content of the specific condensate less than the content of the specific monomer of the light ink composition by 1% by mass or more, preferably 2% by mass or more, preferably 3% by mass or more, and preferably 4 to 10% by mass.

[0073] An ink containing a specific condensate has high moisture retention and excellent clogging recovery property, but has low drying property and is liable to be inferior in rubbing resistance. The light ink composition is often used at a low duty and is liable to dry, so even if it contains a specific condensate, it is likely to have good rubbing resistance. However, by further containing a specific monomer, the balance between viscosity and drying property becomes appropriate, and image quality and rubbing resistance can be preferably balanced. Furthermore, in an ink containing a specific condensate, the viscosity may rapidly increase at the nozzles of an inkjet head, and in that case, landing position deviation is likely to occur during recording. For the purpose of preventing this, it is preferable to use the specific condensate and the specific monomer in combination in the light ink composition. Also, when the light ink composition uses both in combination, it is preferable in that it is easy to match the viscosity with the dark ink composition and it is easier to prevent landing deviation between the light and dark inks.

[0074] On the other hand, the light ink composition may not contain an organic solvent (specific monomer) which is an alkanediol having 2 to 4 carbon atoms in an amount exceeding the content of the organic solvent (specific monomer) which is the alkanediol having 2 to 4 carbon atoms in the dark ink composition, and the light ink composition may not contain the specific monomer. Even in such a case, according to the ink set according to the present embodiment, it is possible to satisfactorily balance image quality and prevention of landing deviation.

[0075] In addition, the content of the specific monomer in the light ink composition is preferably 0.1% by mass or more, more preferably 1% by mass or more, still more preferably 3% by mass or more, and particularly preferably 5% by mass or more with respect to the total mass of the light ink composition. Further, the content of the specific monomer in the light ink composition is preferably 20% by mass or less, more preferably 15% by mass or less, still more preferably 13% by mass or less, and particularly preferably 11% by mass or less with respect to the total mass of the light ink composition. Note that the content of the specific monomer in the light ink composition may be 0% by mass with respect to the total mass of the light ink composition.

[0076] 1.1.3.3 Low molecular weight organic compounds The light ink composition and the dark ink composition included in the ink set according to the present embodiment may each contain a low molecular weight organic compound having a standard boiling point of 150 to 300°C and being any one of amides, sulfur-containing compounds, and cyclic ethers. This is referred to as a specific low molecular weight organic compound. Such a specific low molecular weight organic compound has resin solubility by being any one of amides, sulfur-containing compounds, and cyclic ethers, and may swell and dissolve a resin dispersion or a recording medium contained in the ink, thereby further improving the abrasion resistance. In addition, such a specific low molecular weight organic compound has a standard boiling point of 150 to 300°C, so that the ink tends to dry during recording and has excellent abrasion resistance.

[0077] The molecular weight of the low molecular weight organic compound is preferably 300 or less, and more preferably 50 to 200.

[0078] <Amides> Examples of amides include cyclic amides and acyclic amides. Examples of acyclic amides include alkoxyalkylamides.

[0079] Examples of cyclic amides include lactams, such as pyrrolidones like 2-pyrrolidone (standard boiling point 245 °C), 1-methyl-2-pyrrolidone, 1-ethyl-2-pyrrolidone, 1-propyl-2-pyrrolidone, 1-butyl-2-pyrrolidone, etc., 2-piperidone, ε-caprolactam, N-methyl-ε-caprolactam, N-cyclohexyl-2-pyrrolidone, 5-methyl-2-pyrrolidone, β-propiolactam, ω-heptalactam, succinimide, and the like. Among these, 2-pyrrolidone is particularly preferred.

[0080] Examples of acyclic amides include, for example, alkoxyalkylamides such as 3-methoxy-N,N-dimethylpropionamide, 3-methoxy-N,N-diethylpropionamide, 3-methoxy-N,N-methylethylpropionamide, 3-ethoxy-N,N-dimethylpropionamide, 3-ethoxy-N,N-diethylpropionamide, 3-ethoxy-N,N-methylethylpropionamide, 3-n-butoxy-N,N-dimethylpropionamide, 3-n-butoxy-N,N-diethylpropionamide, 3-n-butoxy-N,N-methylethylpropionamide, 3-n-propoxy-N,N-dimethylpropionamide, 3-n-propoxy-N,N-diethylpropionamide, 3-n-propoxy-N,N-methylethylpropionamide, 3-iso-propoxy-N,N-dimethylpropionamide, 3-iso-propoxy-N,N-diethylpropionamide, 3-iso-propoxy-N,N-methylethylpropionamide, 3-tert-butoxy-N,N-dimethylpropionamide, 3-tert-butoxy-N,N-diethylpropionamide, 3-tert-butoxy-N,N-methylethylpropionamide, etc., N,N-dimethylacetoacetamide, N,N-diethylacetoacetamide, N-methylacetoacetamide, N,N-dimethylisobutyramide, N,N-dimethylformamide, N,N-diethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, N,N-dimethylpropionamide, and the like.

[0081] <Sulfur-containing compounds> Examples of sulfur-containing compounds include sulfoxides, sulfones, and the like.

[0082] Examples of sulfoxides include acyclic sulfoxides such as dimethyl sulfoxide (standard boiling point: 189°C), diethyl sulfoxide, etc., and cyclic sulfoxides such as tetramethylene sulfoxide, etc. Examples of sulfones include cyclic sulfones such as 3-methylsulfolane, sulfolane, etc., and acyclic sulfones such as ethyl isopropyl sulfone, ethyl methyl sulfone, dimethyl sulfone, etc.

[0083] <Cyclic ethers> Examples of cyclic ethers include tetrahydrofuran, 1,4-dioxane, dimethyl isosorbide, 3-methyl-3-oxetanemethanol, 3-ethyl-3-oxetanemethanol (standard boiling point: 220°C), 2-hydroxymethyloxetane, tetrahydrofurfuryl alcohol, glycerol formal, sorbitol ketal, 1,4-dioxane-2,3-diol, dihydrolevoglucosenone, and the like.

[0084] The standard boiling point of the low-molecular organic compound is preferably 150 to 300°C, more preferably 150 to 270°C, and even more preferably 150 to 250°C. When the standard boiling point is within the above range, the drying property is further improved and the abrasion resistance tends to be more excellent.

[0085] The content of the low-molecular organic compound is preferably 3 to 20% by mass, more preferably 5 to 18% by mass, even more preferably 7 to 16% by mass, and particularly preferably 9 to 14% by mass with respect to the total mass of the ink composition.

[0086] 1.1.3.4 Other organic solvents The light ink composition and the dark ink composition included in the ink set according to this embodiment may contain polyhydric alcohols, esters, alkylene glycol ethers, cyclic esters, etc. as organic solvents other than those described above.

[0087] <Polyhydric alcohols> Polyhydric alcohols are compounds having two or more hydroxyl groups in the molecule, and are alkanediols in which alkanes are substituted with two or more hydroxyl groups, or condensates in which alkanediols are condensed between hydroxyl groups intermolecularly. The above-mentioned specific condensates and specific monomers may also correspond to polyhydric alcohols, but here, polyhydric alcohols other than the above-mentioned specific condensates and specific monomers will be described.

[0088] Examples of polyhydric alcohols include alkanediols having 5 or more carbon atoms, organic solvents having 3 or more hydroxyl groups, etc. Examples of alkanediols having 5 or more carbon atoms include 1,2-pentanediol, 1,2-hexanediol, 1,2-heptanediol, 1,2-octanediol, 1,5-pentanediol, 1,6-hexanediol, 2-ethyl-2-methyl-1,3-propanediol, 2-methyl-2-propyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 3-methyl-1,3-butanediol, 2-ethyl-1,3-hexanediol, 3-methyl-1,5-pentanediol, 2-methylpentane-2,4-diol, etc. Examples of organic solvents having 3 or more hydroxyl groups include trimethylolpropane, glycerin, etc.

[0089] <Esters> Examples of the esters include glycol monoacetates such as ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate, diethylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, propylene glycol monomethyl ether acetate, dipropylene glycol monomethyl ether acetate, and methoxybutyl acetate; and glycol diesters such as ethylene glycol diacetate, diethylene glycol diacetate, propylene glycol diacetate, dipropylene glycol diacetate, ethylene glycol acetate propionate, ethylene glycol acetate butyrate, diethylene glycol acetate butyrate, diethylene glycol acetate propionate, diethylene glycol acetate butyrate, propylene glycol acetate propionate, propylene glycol acetate butyrate, dipropylene glycol acetate butyrate, and dipropylene glycol acetate propionate.

[0090] <Alkylene glycol ethers> As the alkylene glycol ethers, monoethers or diethers of alkylene glycol are preferred, and alkyl ethers are more preferred. Specific examples include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, tetraethylene glycol monoethyl ether, tetraethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, tripropylene glycol monobutyl ether and other alkylene glycol monoalkyl ethers, and ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, diethylene glycol methyl ethyl ether, diethylene glycol methyl butyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, triethylene glycol dibutyl ether, triethylene glycol methyl butyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether, tetraethylene glycol dibutyl ether, propylene glycol dimethyl ether, propylene glycol diethyl ether, dipropylene glycol dimethyl ether, dipropylene glycol diethyl ether, tripropylene glycol dimethyl ether and other alkylene glycol dialkyl ethers.

[0091] <Cyclic esters> Examples of cyclic esters include cyclic esters (lactones) such as β-propiolactone, γ-butyrolactone, δ-valerolactone, ε-caprolactone, β-butyrolactone, β-valerolactone, γ-valerolactone, β-hexanolactone, γ-hexanolactone, δ-hexanolactone, β-heptanolactone, γ-heptanolactone, δ-heptanolactone, ε-heptanolactone, γ-octanolactone, δ-octanolactone, ε-octanolactone, δ-nonalactone, ε-nonalactone, ε-decanolactone, etc., and compounds in which the hydrogen of the methylene group adjacent to the carbonyl group thereof is substituted by an alkyl group having 1 to 4 carbon atoms.

[0092] The above organic solvents may be used alone or in combination of two or more.

[0093] For the concentrated ink composition and the light ink composition, the content of the organic solvent with respect to the total mass of the composition is preferably 1 to 40% by mass, more preferably 10 to 30% by mass, and even more preferably 15 to 25% by mass. It is also preferable that the content of the organic solvent having a standard boiling point of 250°C or lower is within the above range.

[0094] For the concentrated ink composition and the light ink composition, it is preferable that each contains 10 to 30% by mass of an organic solvent having a standard boiling point of 250°C or lower with respect to the total mass of the composition. It is preferable that the content of the organic solvent having a standard boiling point exceeding 250°C does not exceed 8% by mass with respect to the total mass of the composition. In such a case, it is preferable because the drying property of the ink composition can be made appropriate and it tends to be more excellent in rubbing resistance. In general, since an organic solvent has a higher viscosity than water and a pinning effect is easily obtained, a method of increasing the content of the organic solvent in the light ink composition for improving the pinning effect can be considered. However, when the content of the organic solvent increases, the drying property tends to decrease and the rubbing resistance tends to be inferior. Therefore, it is preferable that the light ink composition contains a specific condensate and the content of the organic solvent is within the above range, particularly 30% by mass or less, so that the image quality and the rubbing resistance can be balanced well.

[0095] Moreover, it is more preferable that the concentrated ink composition and the light ink composition each contain an organic solvent having a standard boiling point of 250°C or lower in an amount of 15 to 30% by mass based on the total mass of the composition, still more preferably 20 to 30% by mass, and particularly preferably 26 to 30% by mass. Moreover, it is more preferable that the concentrated ink composition and the light ink composition each do not contain an organic solvent having a standard boiling point exceeding 250°C in an amount exceeding 5% by mass based on the total mass of the composition, still more preferably not exceeding 3% by mass, particularly preferably not exceeding 1% by mass, particularly preferably not exceeding 0.5% by mass, and more particularly preferably not containing it.

[0096] Alternatively, it is also preferable that the concentrated ink composition and the light ink composition each have the content of a polyhydric alcohol having a standard boiling point exceeding 250°C within the above range. The organic solvent may include the specific condensate, the specific monomer, the specific low-molecular organic compound, and other organic solvents described above, but is limited to those that are liquid at normal temperature. The organic solvent is preferably a water-soluble organic solvent.

[0097] 1.1.4 Alkanolamines The light ink composition and the concentrated ink composition included in the ink set according to the present embodiment may each contain alkanolamines, and it is preferable that the content of alkanolamines in the light ink composition is larger than that in the concentrated ink composition. Alkanolamines can adjust the pH of the ink composition, and since the viscosity of the ink tends to increase when they are contained, the pinning effect may be improved and the image quality may be improved.

[0098] Examples of alkanolamines include monoethanolamine, diethanolamine, triethanolamine, N,N-dimethylethanolamine, N,N-diethylethanolamine, N,N-dibutylethanolamine, N-aminoethylethanolamine, N-methylethanolamine, N-ethylethanolamine, N-butylethanolamine, N-tert-butylethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, N-butyldiethanolamine, N-tert-butyldiethanolamine, 2-amino-1-propanol, 2-amino-2-methyl-1-propanol, 5-amino-1-pentanol, 2-amino-2-methyl-1,3-propanediol, 2-amino-2-hydroxymethyl-1,3-propanediol, 3-amino-1,2-propanediol, 3-methylamino-1,2-propanediol, propanolamine, N,N-dimethylpropanolamine, N,N-diethylpropanolamine, tripropanolamine, isopropanolamine, diisopropanolamine, triisopropanolamine, N,N-dimethylisopropanolamine, N,N-diethylisopropanolamine, and the like. Note that alkanolamines that are liquid at room temperature are included in the above-mentioned organic solvents.

[0099] The content of alkanolamines in the light ink composition is preferably 5.0% by mass or less, more preferably 4.0% by mass or less, and even more preferably 3.0% by mass or less, based on the total mass of the light ink composition. Also, the content of alkanolamines in the light ink composition is preferably 0.10% by mass or more, more preferably 0.50% by mass or more, even more preferably 1.0% by mass or more, and particularly preferably 1.5% by mass or more, based on the total mass of the light ink composition.

[0100] The content of alkanolamines in the concentrated ink composition is preferably 4.0% by mass or less, more preferably 3.0% by mass or less, and even more preferably 2.0% by mass or less, based on the total mass of the concentrated ink composition. Also, the content of alkanolamines in the concentrated ink composition is preferably 0.05% by mass or more, more preferably 0.25% by mass or more, even more preferably 0.50% by mass or more, and particularly preferably 1.0% by mass or more, based on the total mass of the concentrated ink composition.

[0101] The content of alkanolamines in the light ink composition is preferably higher than that in the concentrated ink composition, preferably 0.5% by mass or more, more preferably 0.8 to 5% by mass higher, and even more preferably 1 to 3% by mass higher.

[0102] 1.1.5 Resin Dispersion The light ink composition and the concentrated ink composition included in the ink set according to this embodiment may each contain a resin dispersion composed of any one of an acrylic resin, a polyurethane resin, a polyester resin, and a polyolefin resin. When the ink composition contains these resin dispersions, it tends to be more excellent in abrasion resistance, which is preferable.

[0103] Examples of the resin of the resin dispersion include acrylic resins, polyurethane resins, fluorene resins, rosin-modified resins, terpene resins, polyester resins, polyolefin resins, polyamide resins, epoxy resins, vinyl chloride resins, ethylene vinyl acetate resins, etc. Among these, it is preferably any one of acrylic resins, polyurethane resins, polyester resins, and polyolefin resins. The resin in the resin dispersion is often handled in the form of an emulsion, but it may also be in the form of a powder.

[0104] An acrylic resin is a general term for polymers obtained by polymerizing at least one acrylic monomer such as (meth)acrylic acid and (meth)acrylic acid ester. Examples include resins obtained from acrylic monomers and copolymers of acrylic monomers and other monomers. For example, acrylic-vinyl resins, which are copolymers of acrylic monomers and vinyl monomers, can be mentioned. Further examples include copolymers with vinyl monomers such as styrene. As acrylic monomers, acrylamide, acrylonitrile, etc. can also be used.

[0105] Commercially available products may be used for the resin emulsion made from acrylic resin. For example, it may be selected from among FK-854, Mobinyl 952B, 718A (trade names, manufactured by Japan Coating Resin Co., Ltd.), Nipol LX852, LX874 (trade names, manufactured by Nippon Zeon Co., Ltd.), Polyzol AT860 (manufactured by Showa Denko K.K.), Boncoat AN-1190S, YG-651, AC-501, AN-1170, 4001 (trade names, acrylic resin emulsion manufactured by DIC Corporation), etc. and used.

[0106] In this specification, the acrylic resin may be a styrene-acrylic resin as described above. Also, in this specification, the notation (meth)acrylic means at least one of acrylic and methacrylic.

[0107] Styrene acrylic resin is a copolymer obtained from styrene monomer and acrylic monomer, and examples include styrene-acrylic acid copolymer, styrene-methacrylic acid copolymer, styrene-methacrylic acid-acrylic acid ester copolymer, styrene-α-methylstyrene-acrylic acid copolymer, styrene-α-methylstyrene-acrylic acid-acrylic acid ester copolymer, etc. For styrene acrylic resin, commercially available products can be used, for example, Joncryl 62J, 7100, 390, 711, 511, 7001, 631, 632, 741, 450, 840, 74J, HRC-1645J, 734, 852, 7600, 775, 537J, 1535, PDX-7630A, 352J, 352D, PDX-7145, 538J, 7640, 7641, 631, 790, 780, 7610 (trade name, manufactured by BASF), Mobinyl 966A, 975N (trade name, manufactured by Japan Coating Resin Co., Ltd.), etc.

[0108] Polyurethane resin is a general term for resins having urethane bonds. In addition to urethane bonds, for polyurethane resin, polyether type urethane resin containing an ether bond in the main chain, polyester type urethane resin containing an ester bond in the main chain, polycarbonate type urethane resin containing a carbonate bond in the main chain, etc. can also be used. As the polyurethane resin, commercially available products can be used, for example, selected from commercially available products such as Superflex 210, 460, 460s, 840, E-4000 (trade name, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), Rezamin D-1060, D-2020, D-4080, D-4200, D-6300, D-6455 (trade name, manufactured by Dainichi Seiko Kogyo Co., Ltd.), Takelac WS-6020, WS-6021, W-512-A-6 (trade name, manufactured by Mitsui Chemicals Polyurethane Co., Ltd.), Sankure 2710 (trade name, manufactured by Lubrizol), Permaline UA-150 (trade name, manufactured by Sanyo Chemical Industries, Ltd.), etc.

[0109] The polyester resin is not particularly limited, and examples thereof include polyethylene terephthalate. As the polyester resin, commercially available products may be used, and examples thereof include Elier KT8701 (trade name, manufactured by Unitika Ltd.).

[0110] The polyolefin resin is, for example, a resin produced from olefins such as ethylene, propylene, and butylene or derivatives thereof, and specifically includes polyethylene resins, polypropylene resins, polybutylene resins, and the like.

[0111] Commercially available polyolefin resins include, for example, AQUACER series such as AQUACER513 (polyethylene resin, average particle diameter of 100 nm or more and 200 nm or less, melting point of 130 °C, solid content of 30%), AQUACER507, AQUACER515, AQUACER840, AQUACER1547 (above are trade names, manufactured by BYK-Chemie Japan Co., Ltd.), and high-tech series such as High-Tech E-7025P, High-Tech E-2213, High-Tech E-6500, High-Tech E-6314, High-Tech E-9460, High-Tech E-9015, High-Tech E-4A, High-Tech E-5403P, High-Tech E-8237 (above are trade names, manufactured by Toho Chemical Co., Ltd., polyethylene resin), and Nopcoat PEM-17 (trade name, manufactured by San Nopco Ltd., polyethylene emulsion, average particle diameter of 40 nm), and the like.

[0112] In addition, the resin of the resin dispersion may be supplied in the form of an emulsion. Examples of commercially available products of such resin emulsions include Microgel E-1002, E-5002 (trade names of products manufactured by Nippon Paint Co., Ltd., styrene-acrylic resin emulsions), Boncoat AN-1190S, YG-651, AC-501, AN-1170, 4001, 5454 (trade names of products manufactured by DIC Corporation, styrene-acrylic resin emulsions), Polyzol AM-710, AM-920, AM-2300, AP-4735, AT-860, PSASE-4210E (acrylic resin emulsion), Polyzol AP-7020 (styrene-acrylic resin emulsion), Polyzol SH-502 (vinyl acetate resin emulsion), Polyzol AD-13, AD-2, AD-10, AD-96, AD-17, AD-70 (ethylene-vinyl acetate resin emulsion), Polyzol PSASE-6010 (ethylene-vinyl acetate resin emulsion) (trade name of a product manufactured by Showa Denko K.K.), Polyzol SAE1014 (trade name, styrene-acrylic resin emulsion, manufactured by Nippon Zeon Co., Ltd.), Cybinol SK-200 (trade name, acrylic resin emulsion, manufactured by Saiden Chemical Co., Ltd.), AE-120A (trade name of a product manufactured by JSR Corporation, acrylic resin emulsion), AE373D (trade name of a product manufactured by E-Tech Co., Ltd., carboxy-modified styrene-acrylic resin emulsion), Seikadine 1900W (trade name of a product manufactured by Dainichi Seika Kogyo Co., Ltd., ethylene-vinyl acetate resin emulsion), Vinibran 2682 (acrylic resin emulsion), Vinibran 2886 (vinyl acetate-acrylic resin emulsion), Vinibran 5202 (acrylic acetate resin emulsion) (trade names of products manufactured by Nisshin Chemical Industry Co., Ltd.), Vinibran 700, 2586 (manufactured by Nisshin Chemical Industry Co., Ltd.), Elitel KA-5071S, KT-8803, KT-9204, KT-8701, KT-8904, KT-0507 (trade names of products manufactured by Unitika Ltd., polyester resin emulsions), Hi-Tech SN-2002 (trade name of a product manufactured by Toho Chemical Co., Ltd., polyester resin emulsion), Takelac W-6020, W-635, W-6061, W-605, W-635, W-6021 (trade names of products manufactured by Mitsui Chemicals Polyurethane Co., Ltd., urethane resin emulsions), Superflex 870, 800, 150, 420, 460, 470, 610, 620, 700 (trade names of products manufactured by Daiichi Kogyo Seiyaku Co., Ltd.,Urethane resin emulsion), Permalin UA-150 (manufactured by Sanyo Chemical Industries, Ltd., urethane resin emulsion), Sun Cure 2710 (manufactured by Lubrizol Japan, urethane resin emulsion), NeoRez R-9660, R-9637, R-940 (manufactured by Kusumoto Chemical Co., Ltd., urethane resin emulsion), Adeka Bon Titer HUX-380, 290K (manufactured by ADEKA Corporation, urethane resin emulsion), Mobinyl 966A, Mobinyl 7320 (manufactured by Japan Coating Resin Co., Ltd.), Joncryl 7100, 390, 711, 511, 7001, 632, 741, 450, 840, 74J, HRC-1645J, 734, 852, 7600, 775, 537J, 1535, PDX-7630A, 352J, 352D, PDX-7145, 538J, 7640, 7641, 631, 790, 780, 7610 (above, manufactured by BASF), NK Binder R-5HN (manufactured by Shin-Nakamura Chemical Co., Ltd.), Hydran WLS-210 (non-crosslinked polyurethane: manufactured by DIC Corporation), Joncryl 7610 (manufactured by BASF), etc. may be selected and used.

[0113] The resin of the resin dispersion may be used alone or in combination of two or more.

[0114] The glass transition temperature (Tg) of the resin of the resin dispersion is preferably 150 °C or lower, more preferably 120 °C or lower, in terms of being easily film-formed on the recording medium and having excellent adhesion, resulting in more excellent abrasion resistance. On the other hand, in terms of more excellent abrasion resistance due to having hardness and more excellent anti-blocking and back printing, it is preferably -50 °C or higher, more preferably 0 °C or higher, and further preferably 20 °C or higher. The glass transition temperature (Tg) can be confirmed by a standard method using differential scanning calorimetry (DSC) or the like.

[0115] When the resin dispersion is contained, the content is 0.1% by mass or more and 20% by mass or less, preferably 1.0% by mass or more and 15.0% by mass or less, more preferably 2.0% by mass or more and 10.0% by mass or less, and further preferably 3.0% by mass or more and 8.0% by mass or less, in terms of the total mass of the ink composition on a solid content basis.

[0116] 1.1.6 Surfactant The light ink composition and the concentrated ink composition included in the ink set according to this embodiment may each contain a surfactant. The surfactant has a function of reducing the surface tension of the ink composition and improving the wettability with the recording medium and the substrate. Among surfactants, acetylene glycol-based surfactants, silicone-based surfactants, and fluorine-based surfactants can be preferably used.

[0117] The acetylene glycol-based surfactant is not particularly limited. For example, Surfynol 104, 104E, 104H, 104A, 104BC, 104DPM, 104PA, 104PG-50, 104S, 420, 440, 465, 485, SE, SE-F, 504, 61, DF37, CT111, CT121, CT131, CT136, TG, GA, DF110D (all of the above are product names, manufactured by Air Products & Chemicals, Inc.), Orfin B, Y, P, A, STG, SPC, E1004, E1010, PD-001, PD-002W, PD-003, PD-004, EXP.4001, EXP.4036, EXP.4051, AF-103, AF-104, AK-02, SK-14, AE-3 (all of the above are product names, manufactured by Nissin Chemical Industry Co., Ltd.), Acetylenol E00, E00P, E40, E100 (all of the above are product names, manufactured by Kawaken Fine Chemicals Co., Ltd.) can be mentioned.

[0118] As the silicone surfactant, although not particularly limited, polysiloxane compounds are preferably mentioned. As the polysiloxane compound, although not particularly limited, for example, polyether-modified organosiloxane is mentioned. As commercially available products of the polyether-modified organosiloxane, for example, BYK-306, BYK-307, BYK-333, BYK-341, BYK-345, BYK-346, BYK-348, BYK-349, BYK-3420, BYK-3480, BYK-3481 (the above trade names, manufactured by Big Chemie Japan), KF-351A, KF-352A, KF-353, KF-354L, KF-355A, KF-615A, KF-945, KF-640, KF-642, KF-643, KF-6020, X-22-4515, KF-6011, KF-6012, KF-6015, KF-6017 (the above trade names, manufactured by Shin-Etsu Chemical Co., Ltd.) are mentioned.

[0119] As the fluorine surfactant, it is preferable to use a fluorine-modified polymer. Specific examples include BYK-3440 (manufactured by Big Chemie Japan), Surflon S-241, S-242, S-243 (the above trade names, manufactured by AGC Seimi Chemical Co., Ltd.), Fluorigent 215M (manufactured by Neos Co., Ltd.), etc.

[0120] When the ink composition contains a surfactant, a plurality of types may be contained. When the ink composition contains a surfactant, the content is preferably 0.1% by mass or more and 2.0% by mass or less, more preferably 0.2% by mass or more and 1.5% by mass or less, and still more preferably 0.3% by mass or more and 1.0% by mass or less with respect to the total mass of the ink composition.

[0121] 1.1.7 Other Components The light ink composition and the concentrated ink composition included in the ink set according to the present embodiment may each appropriately add various additives such as an antifoaming agent, a dissolution aid, a viscosity modifier, a pH adjuster, an antioxidant, a preservative, an antifungal agent, a corrosion inhibitor, a humectant other than an organic solvent, and a chelating agent for capturing metal ions that affect dispersion.

[0122] 1.1.8 Method for Preparing Ink Composition The light ink composition and the dark ink composition included in the ink set according to this embodiment are obtained by mixing the above-described components in an arbitrary order and, if necessary, filtering etc. to remove impurities. As a method for mixing each component, a method of sequentially adding materials to a container equipped with a stirring device such as a mechanical stirrer or a magnetic stirrer and stirring and mixing is preferably used. As a filtering method, centrifugal filtration, filter filtration etc. can be performed as necessary.

[0123] 1.1.9 Physical Properties of Ink Composition From the viewpoint of the balance between image quality and reliability as an ink for inkjet recording, the surface tension at 20°C of the light ink composition and the dark ink composition included in the ink set according to this embodiment is preferably 18 mN / m or more and 40 mN / m or less, more preferably 20 mN / m or more and 35 mN / m or less, and even more preferably 22 mN / m or more and 33 mN / m or less. The surface tension can be measured, for example, by using an automatic surface tension meter CBVP-Z (trade name, manufactured by Kyowa Interface Science Co., Ltd.) and checking the surface tension when a platinum plate is wetted with the ink in an environment of 20°C.

[0124] Also, from the same viewpoint, the viscosity at 20°C of the ink composition according to this embodiment is preferably 3 mPa·s or more and 10 mPa·s or less, and more preferably 3 mPa·s or more and 8 mPa·s or less. The viscosity can be measured, for example, by using a viscoelasticity tester MCR-300 (trade name, manufactured by Pysica) and measuring the viscosity in an environment of 20°C.

[0125] 1.2 Treatment Liquid The treatment liquid included in the ink set according to this embodiment contains a flocculant.

[0126] In addition, in this embodiment, the processing liquid is an auxiliary liquid that is applied to the recording medium before or after applying the above-described concentrated ink composition and diluted ink composition to the recording medium. The processing liquid may or may not contain the above-described coloring material, but the content of the coloring material is preferably 0.2% by mass or less, more preferably 0.1% by mass or less, and even more preferably 0.05% by mass or less. It is particularly preferable not to contain a coloring material. The processing liquid is preferably an aqueous composition.

[0127] 1.2.1 Flocculant The processing liquid included in the ink set according to this embodiment contains a flocculant. By including a flocculant in the processing liquid, in the ink adhesion step described later, the flocculant and the coloring material and the like contained in the ink composition react promptly. Then, the dispersion state of the coloring material and the like in the ink composition is disrupted, the coloring material aggregates, and this aggregate inhibits the penetration of the coloring material into the recording medium, so it is considered to be excellent in terms of improving the image quality of the recorded image.

[0128] Examples of the flocculant include polyvalent metal salts, organic acids, cationic compounds (cationic resins, cationic surfactants, etc.). These flocculants may be used alone or in combination of two or more. Among these flocculants, it is preferable to use at least one flocculant selected from the group consisting of polyvalent metal salts and cationic resins because of its excellent reactivity with the coloring material and the like contained in the ink composition.

[0129] The polyvalent metal salt is composed of polyvalent metal ions of divalent or higher and anions that bind to these polyvalent metal ions, and is a compound soluble in water. Specific examples of polyvalent metal ions include divalent metal ions such as Ca 2+ , Cu 2+ , Ni 2+ , Mg 2+ , Zn 2+ , Ba 2+ ; trivalent metal ions such as Al 3+ , Fe 3+ , Cr 3+ . Examples of the anion include Cl - , I -, Br - , SO4 2- , ClO 3- , NO 3- , and HCOO - , CH3COO - Examples include etc. Among these polyvalent metal salts, calcium salts and magnesium salts are preferred from the viewpoints of the stability of the treatment liquid and the reactivity as a flocculant.

[0130] Examples of the organic acid include, for example, phosphoric acid, polyacrylic acid, acetic acid, glycolic acid, malonic acid, malic acid, maleic acid, ascorbic acid, succinic acid, glutaric acid, fumaric acid, citric acid, tartaric acid, lactic acid, sulfonic acid, orthophosphoric acid, pyrrolidonecarboxylic acid, pyronecarboxylic acid, pyrrolecarboxylic acid, furancarboxylic acid, pyridinecarboxylic acid, coumaric acid, thiophenecarboxylic acid, nicotinic acid, or derivatives of these compounds, or salts thereof, etc. are preferably mentioned. The organic acid may be used alone or in combination of two or more.

[0131] Examples of the cationic resin include, for example, cationic urethane resin, cationic olefin resin, cationic allylamine resin, polyamine resin, quaternary ammonium salt polymer, etc.

[0132] As the cationic urethane resin, known ones can be appropriately selected and used. As the cationic urethane resin, commercially available products can be used. For example, Hydran CP-7010, CP-7020, CP-7030, CP-7040, CP-7050, CP-7060, CP-7610 (above trade names, manufactured by Dainippon Ink and Chemicals, Inc.), Superflex 600, 610, 620, 630, 640, 650 (above trade names, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), Urethane Emulsion WBR-2120C, WBR-2122C (above trade names, manufactured by Daisheng Fine Chemical Co., Ltd.), etc. can be used.

[0133] The cationic olefin resin has olefins such as ethylene and propylene in its structural skeleton, and known ones can be appropriately selected and used. Further, the cationic olefin resin may be in an emulsion state dispersed in a solvent containing water, an organic solvent, or the like. As the cationic olefin resin, commercially available products can be used, and examples thereof include Arrowbase CB-1200 and CD-1200 (the above are trade names, manufactured by Unitika Ltd.).

[0134] As the cationic allylamine resin, known ones can be appropriately selected and used. For example, polyallylamine hydrochloride, polyallylamine amide sulfate, allylamine hydrochloride / diallylamine hydrochloride copolymer, allylamine acetate / diallylamine acetate copolymer, allylamine acetate / diallylamine acetate copolymer, allylamine hydrochloride / dimethylallylamine hydrochloride copolymer, allylamine / dimethylallylamine copolymer, polydiallylamine hydrochloride, polymethyldiallylamine hydrochloride, polymethyldiallylamine amide sulfate, polymethyldiallylamine acetate, polydiallyldimethylammonium chloride, diallylamine acetate / sulfur dioxide copolymer, diallylmethylethylammonium ethyl sulfate / sulfur dioxide copolymer, methyldiallylamine hydrochloride / sulfur dioxide copolymer, diallyldimethylammonium chloride / sulfur dioxide copolymer, diallyldimethylammonium chloride / acrylamide copolymer, etc. can be mentioned. As such cationic allylamine resins, commercially available products can be used. For example, PAA-HCL-01, PAA-HCL-03, PAA-HCL-05, PAA-HCL-3L, PAA-HCL-10L, PAA-H-HCL, PAA-SA, PAA-01, PAA-03, PAA-05, PAA-08, PAA-15, PAA-15C, PAA-25, PAA-H-10C, PAA-D11-HCL, PAA-D41-HCL, PAA-D19-HCL, PAS-21CL, PAS-M-1L, PAS-M-1, PAS-22SA, PAS-M-1A, PAS-92, PAS-92A, (the above are trade names, manufactured by Nitto Bo Medical Co., Ltd.), Hymol Neo-600, Hymolock Q-101, Q-311, Q-501, Hymax SC-505, SC-505 (the above are trade names, manufactured by Hymol Co., Ltd.), etc. can be used.

[0135] Examples of quaternary ammonium salt polymers include amine-epichlorohydrin copolymers, poly(2-hydroxy-3-methacryloxypropyltrimethylammonium chloride), poly(2-hydroxy-3-methacryloxypropyltriethylammonium chloride), poly(2-hydroxy-3-acryloxypropyltrimethylammonium chloride), poly(2-hydroxy-3-acryloxypropyltriethylammonium chloride), poly(2-methacryloxyethyltrimethylammonium chloride), poly(2-methacryloxyethyltriethylammonium chloride), poly(2-acryloxyethyltrimethylammonium chloride), poly(2-acryloxyethyltriethylammonium chloride), salts of poly(dimethylaminoethyl methacrylate), salts of poly(diethylaminoethyl methacrylate), salts of poly(diethylaminoethyl acrylate), salts of poly(dimethylaminoethyl methacrylate), salts of poly(dimethylaminoethyl acrylate), poly(4-vinyl-N-methylpyridinium chloride), N,N-dimethyl-substituted 3,5-methylpiperidinium chloride resin, poly(dimethyldiallylammonium chloride), and poly(diethyldiallylammonium chloride) polyethyleneimine hydrochloride, etc.

[0136] Commercially available quaternary ammonium salt polymers can also be used. For example, Cation Master PD-7 (manufactured by Yokkaichi Gosei Co., Ltd., amine-epichlorohydrin copolymer), PAS-H-1L, PAS-H-5L, PAS-H-10L; PAS-24; PAS-2401; PAS-A-1, PAS-A-5; PAS-J-81L, PAS-J-81, PAS-J-41 (manufactured by Nitto Boehringer Medical Co., Ltd.), Papigen P-105, Miligen P-20 (manufactured by Senka Co., Ltd.), etc.

[0137] Examples of cationic surfactants include primary, secondary, and tertiary amine salt type compounds, alkylamine salts, dialkylamine salts, aliphatic amine salts, benzalkonium salts, quaternary ammonium salts, quaternary alkylammonium salts, alkylpyridinium salts, sulfonium salts, phosphonium salts, onium salts, imidazolinium salts, and the like. Specific examples of cationic surfactants include hydrochlorides, acetates, etc. of laurylamine, coconut amine, rosin amine, etc., lauryltrimethylammonium chloride, cetyltrimethylammonium chloride, benzyltributylammonium chloride, benzalkonium chloride, dimethylethyllaurylammonium ethyl sulfate, dimethylethyloctylammonium ethyl sulfate, trimethyllaurylammonium hydrochloride, cetylpyridinium chloride, cetylpyridinium bromide, dihydroxyethyllaurylamine, decyldimethylbenzylammonium chloride, dodecyldimethylbenzylammonium chloride, tetradecyldimethylammonium chloride, hexadecyldimethylammonium chloride, octadecyldimethylammonium chloride, and the like.

[0138] The flocculant may be used alone or in combination of two or more.

[0139] The content of the flocculant may be, for example, 0.1% by mass or more and 25% by mass or less, 1% by mass or more and 20% by mass or less, or 3% by mass or more and 10% by mass or less based on the total mass (100% by mass) of the treatment liquid.

[0140] 1.2.2 Water The treatment liquid included in the ink set according to this embodiment may contain water. As the water, the same water as exemplified in the above ink composition can be used. The content of water contained in the treatment liquid can be, for example, 40% by mass or more, preferably 50% by mass or more, more preferably 60% by mass or more, and still more preferably 70% by mass or more based on the total mass of the treatment liquid.

[0141] 1.2.3 Organic solvent The processing liquid included in the ink set according to this embodiment may contain an organic solvent. As the organic solvent, the same solvents as those exemplified in the above ink composition can be used. The content of the organic solvent is not particularly limited, but can be, for example, 10% by mass or more and 80% by mass or less, preferably 15% by mass or more and 70% by mass or less, based on the total mass of the processing liquid.

[0142] The standard boiling point of the organic solvent can be contained independently of the standard boiling point of the organic solvent that may be contained in the ink composition at a temperature within the preferable range of the standard boiling point of the organic solvent that may be contained in the above ink composition. Alternatively, the standard boiling point of the organic solvent is preferably 180°C or higher, more preferably 190°C or higher, and even more preferably 200°C or higher. Also, the standard boiling point of the organic solvent is preferably 300°C or lower, more preferably 270°C or lower, and even more preferably 250°C or lower.

[0143] 1.2.4 Alkanolamines The processing liquid included in the ink set according to this embodiment may contain alkanolamines. As the alkanolamines, the same alkanolamines as those exemplified in the above ink composition can be used. The content of the alkanolamines is preferably, for example, 0.01% by mass to 5% by mass, more preferably 0.03% by mass to 3% by mass, even more preferably 0.05% by mass to 1% by mass, and particularly preferably 0.07% by mass to 0.5% by mass, based on the total mass of the processing liquid.

[0144] 1.2.5 Surfactants The processing liquid included in the ink set according to this embodiment may contain a surfactant. As the surfactant, the same surfactants as those exemplified in the above ink composition can be used. The content of the surfactant in the processing liquid can also be the same as that in the above ink composition.

[0145] 1.2.6 Other Components The processing liquid included in the ink set according to this embodiment may include each component that can be contained in the above-described ink composition, such as a resin dispersion, an antifoaming agent, a dissolution aid, a viscosity modifier, a pH adjuster, an antioxidant, a preservative, a fungicide, a corrosion inhibitor, a humectant that is not an organic solvent, and a chelating agent for capturing metal ions that affect dispersion. These components and their contents can be the same as those of the above-described ink composition.

[0146] 1.2.7 Method for Adjusting Processing Liquid and Physical Properties Since the method for adjusting the processing liquid and the physical properties included in the ink set according to this embodiment can be the same as those of the above-described ink composition, the description thereof is omitted.

[0147] 1.3 Uses of Ink Set The ink set according to this embodiment is preferably used for recording on a low-absorbency recording medium or a non-absorbency recording medium.

[0148] In the recording using the ink set according to this embodiment, the recording medium for forming an image is not particularly limited. Therefore, examples of the recording medium include absorbent recording media such as paper, film, and cloth, low-absorbency recording media such as printed paper, and non-absorbent recording media such as metal, glass, and polymer. However, the ink set according to this embodiment is preferably used for recording on a low-absorbency recording medium or a non-absorbency recording medium because the effects of the present invention can be more enjoyed. That is, compared with absorbent recording media, low-absorbency recording media or non-absorbent recording media are more likely to cause ink droplets to gather and bleed because the ink is difficult to dry, resulting in inferior image quality and inferior abrasion resistance. However, according to the ink set according to this embodiment, even in the case of recording on such a recording medium, good abrasion resistance can be achieved, and both excellent image quality and prevention of landing deviation can be achieved.

[0149] A low-absorbing recording medium or a non-absorbing recording medium refers to a recording medium that does not absorb or hardly absorbs a liquid such as an ink composition. Quantitatively, a low-absorbing recording medium or a non-absorbing recording medium refers to a recording medium in which the water absorption amount from the start of contact to 30 msec 1 / 2 is 10 mL / m 2 or less in the Bristow method. This Bristow method is the most popular method for measuring the liquid absorption amount in a short time and is also adopted by the Japan Tappi Pulp Technology Association: JAPAN TAPPI. Details of the test method are described in Standard No. 51, "Paper and Paperboard - Liquid Absorbency Test Method - Bristow Method" of "JAPAN TAPPI Paper Pulp Test Method 2000 Edition". On the other hand, an absorbent recording medium refers to a recording medium that does not fall under non-absorbent and low-absorbent.

[0150] Examples of non-absorbing recording media include those with a recording surface made of plastic. Here, the surface of the recording surface does not have an absorption layer or a receiving layer for absorbing a liquid. For example, those in which plastic is coated on a base material such as paper, those in which a plastic film is adhered to a base material such as paper, and plastic films without an absorption layer or a receiving layer can be mentioned. Plastics mentioned here include polyvinyl chloride, polyethylene terephthalate, polycarbonate, polystyrene, polyurethane, polyethylene, polypropylene, and the like.

[0151] Examples of low-absorbing recording media include recording media called coated papers with a coating layer provided on the surface. For example, as those with a paper base material, printed papers such as art paper, coated paper, and matte paper can be mentioned. When the base material is a plastic film, those in which a hydrophilic polymer or the like is coated on the surface of polyvinyl chloride, polyethylene terephthalate, polycarbonate, polystyrene, polyurethane, polyethylene, polypropylene, etc., and those in which particles such as silica and titanium are coated together with a binder can be mentioned.

[0152] The ink set according to this embodiment can also be suitably used for recording on a flexible packaging film. The flexible packaging film is one aspect of the non-absorbent recording medium described above. More specifically, the flexible packaging film is a flexible film material used for food packaging, toiletries, cosmetics packaging, etc., a material having anti-fogging properties and antistatic properties, an antioxidant, etc. are present on the film surface, and it is a film material having a thickness in the range of 5 to 70 μm, preferably 10 to 50 μm. When the ink composition is adhered to this film, the ink composition is more difficult to fix and bleed compared to a plastic film of normal thickness, and thus the image quality may be inferior. However, the ink set according to this embodiment tends to be able to obtain excellent image quality even on a flexible packaging film.

[0153] As the material constituting the recording surface of the flexible packaging film, those containing at least one resin selected from olefin resins such as polyethylene and polypropylene, ester resins such as polyester, vinyl chloride resins such as polyvinyl chloride, and amide resins such as polyamide can be used. As the film base material including the recording surface of the flexible packaging film, those obtained by processing these resins into a film or sheet shape can be used. In the case of a film or sheet using a resin, any of an unstretched film, a stretched film stretched in one axial direction or two axial directions, etc. can be used, and it is preferable to use a film stretched in two axial directions. Further, if necessary, it can also be used in a laminated state in which films or sheets made of these various resins are laminated.

[0154] In addition, the ink set according to this embodiment can also be suitably used for recording on a recording medium for signgraphics. As the recording medium for signgraphics, the materials vary widely, such as banners, coated paper, matte paper, wallpaper, cloth, and plastic films such as PET and PVC. In particular, it can be suitably used for transparent or translucent plastic films used for window displays, car wrapping, etc. These films are often composed of flexible polyolefin, PET, PVC, etc. as the base material, and have an adhesive layer on the opposite side of the printing surface. After printing, they are attached to window glass, vehicle bodies, etc. on the adhesive surface for use. When ink is applied to this film, the ink is more difficult to fix and tends to bleed, so the image quality may be inferior. However, the ink set according to this embodiment tends to be able to obtain excellent image quality even on a recording medium for signgraphics.

[0155] As the material constituting the recording surface of the film for signgraphics, those containing at least one resin selected from olefin resins such as polyethylene and polypropylene, ester resins such as polyester, vinyl chloride resins such as polyvinyl chloride, and amide resins such as polyamide can be used.

[0156] Note that the recording medium may be colorless transparent, translucent, colored transparent, colored opaque, colorless opaque, etc.

[0157] 2. Recording method The recording method according to an embodiment of the present invention is In the recording method using the above-described ink set, It includes a step of attaching the treatment liquid to the recording medium and a step of attaching the light ink composition and the concentrated ink composition to the recording medium by an inkjet method.

[0158] According to the recording method according to this embodiment, excellent image quality can be obtained, and landing deviation can be excellently reduced.

[0159] Since light ink generally contains less coloring material, which is an aggregating component, than dark ink, its reactivity with the treatment liquid is lower than that of dark ink, and the image quality obtained by a recording method using light ink tends to be insufficient. Further, even if the image quality of light ink can be improved, it is difficult to match the ejection characteristics of light ink and dark ink, and there has been a problem that landing deviation occurs when both are ejected simultaneously. Now, by including, in the light ink composition included in the ink set used in the recording method, an organic solvent (specific condensate) that is a condensate of an alkanediol having 2 or 3 carbon atoms and has two hydroxyl groups, excellent image quality has been obtained. This is because, by including a specific condensate having a relatively high viscosity, when the drying of the light ink composition adhered to the recording medium progresses, the ink greatly thickens, and the movement of the ink droplets is further suppressed. That is, due to the fixing effect (pinning effect) of the ink droplets on the recording medium by the reaction with the treatment liquid and the pinning effect due to the thickening of the ink droplets themselves, the ink droplets can be fixed before they gather and bleed, and thus excellent image quality has been obtained. Furthermore, by including, in the dark ink composition included in the ink set used in the recording method, an organic solvent (specific monomer) that is an alkanediol having 2 to 4 carbon atoms, it has become possible to match the ejection characteristics of the dark ink composition and the light ink composition and excellently reduce landing deviation. This is presumably because the specific condensate contained in the light ink composition and the specific monomer contained in the dark ink composition are similar compounds, and therefore, their ejection characteristics (especially viscosity) have also become similar. Also, when the content of the coloring material contained in the ink is small, the viscosity tends to be low, but it is also presumably because when the light ink composition contains a specific condensate, the viscosity becomes appropriate and the ejection characteristics are likely to match.

[0160] Hereinafter, each step included in the recording method according to the present embodiment and the inkjet recording apparatus applicable to the recording method will be described.

[0161] 2.1 Treatment liquid adhesion step The recording method according to this embodiment includes a step of attaching the processing liquid included in the above-described ink set to a recording medium (processing liquid attachment step).

[0162] The method of attaching the processing liquid to the recording medium is not particularly limited. For example, methods such as applying the processing liquid with a roll coater or the like, spraying the processing liquid with a spray or the like, and applying the processing liquid by an inkjet method can be mentioned. Among these, it is preferable to attach the processing liquid to the recording medium by an inkjet method. This is because it can be selectively attached only to the necessary parts, so it is preferable because it tends to be excellent in reducing the amount of liquid used, that is, the printing cost, shortening the drying time, etc. When applying the processing liquid by an inkjet method, for example, it can be performed by discharging with an inkjet head 2 using an inkjet recording apparatus 1 as shown in FIG. 1.

[0163] As the recording medium, the same recording medium as that exemplified as the recording medium that can be used for the above-described ink set can be used, and a low-absorbency recording medium or a non-absorbency recording medium is more preferable.

[0164] The processing liquid attachment step may be before the attachment of the ink composition, after the attachment of the ink composition, or at the same time as the attachment of the ink composition. When attaching the processing liquid before the attachment of the ink composition or at the same time as the attachment of the ink composition, it is preferable that the recording medium is heated by a preheater 7 as shown in FIG. 1 before the processing liquid attachment step or by an IR heater 3 or a platen heater 4 as shown in FIG. 1 during the processing liquid attachment step. By attaching the processing liquid onto the heated recording medium, the processing liquid discharged onto the recording medium is likely to spread and be evenly applied on the recording medium in some cases. As a result, the ink composition and the processing liquid attached in the ink attachment step described later tend to react sufficiently, and excellent image quality is likely to be obtained. Further, since the processing liquid is evenly applied on the recording medium M, the amount of its application can be reduced, and it may be possible to prevent a decrease in the rub resistance of the obtained image.

[0165] The amount of the treatment liquid adhered is preferably 0.1 to 5 mg / inch per unit area of the recording area of the recording medium 2 and more preferably 0.3 to 4 mg / inch 2 even more preferably 0.5 to 3 mg / inch 2 and still more preferably 0.7 to 2 mg / inch 2 and particularly preferably so. The amount of the treatment liquid adhered may be the maximum amount adhered per unit area of the recording area of the recording medium, which is preferable.

[0166] The surface temperature of the recording medium when the treatment liquid is adhered can be set independently of the preferable range of the surface temperature (primary heating temperature) of the recording medium when the ink described later is adhered. For example, the surface temperature of the recording medium when the treatment liquid is adhered is preferably 45°C or lower, more preferably 40°C or lower, and still more preferably 38°C or lower. Further, the lower limit value of the surface temperature of the recording medium when the treatment liquid is adhered is preferably 25°C or higher, more preferably 30°C or higher, and even more preferably 32°C or higher. When the surface temperature of the recording medium when the treatment liquid is adhered is within the above range, the treatment liquid can be uniformly applied to the recording medium, and there is a tendency to improve the abrasion resistance and image quality. Further, when using the inkjet recording apparatus 1 as shown in FIG. 1, the influence of heat on the inkjet head 2 may be suppressed.

[0167] 2.2 Ink Adhesion Step The recording method according to the present embodiment includes a step (ink adhesion step) of adhering a light ink composition and a dark ink composition to a recording medium by an inkjet method.

[0168] The ink adhesion step is a step of ejecting and adhering the light ink composition and the dark ink composition provided in the above-described ink set. When using an inkjet recording apparatus 1 as shown in FIG. 1, for example, an image composed of the light ink composition and the dark ink composition is formed on the surface of the recording medium through this step. The recording area, which is the area where recording is performed on the recording medium, has an area where both the treatment liquid and the ink composition are adhered, and the ink composition includes at least one of the light ink composition and the dark ink composition. Also, the area where the light ink composition is adhered and the area where the dark ink composition is adhered in the recording area may be separate areas. And / or, both the light ink composition and the dark ink composition may be adhered to the same area.

[0169] In the present embodiment, the ink adhesion step may include a step of adhering the light ink composition provided in the above-described ink set to the recording medium by an inkjet method and a step of adhering the dark ink composition to the recording medium by an inkjet method. The step of adhering the light ink composition to the recording medium and the step of adhering the dark ink composition to the recording medium may or may not be simultaneous.

[0170] The adhesion amount of the light ink composition is preferably 0.5 to 20 mg / inch per unit area of the recording area of the recording medium 2 more preferably 1 to 15 mg / inch 2 even more preferably 2 to 10 mg / inch 2 still more preferably 3 to 8 mg / inch 2 and particularly preferably 3 to 8 mg / inch. The adhesion amount of the dark ink composition is preferably 1 to 40 mg / inch per unit area of the recording area of the recording medium 2 more preferably 2 to 30 mg / inch 2 even more preferably 4 to 20 mg / inch 2 still more preferably 6 to 16 mg / inch 2 and particularly preferably 6 to 16 mg / inch. The adhesion amount of each of the above ink compositions may be, and is preferably, the maximum adhesion amount per unit area of the recording region of the recording medium. Also, the adhesion amount ratio (A / B) of the adhesion amount (A) of the light ink composition and the adhesion amount (B) of the dark ink composition is preferably 0.3 to 0.7.

[0171] 2.3 Primary heating step The recording method according to the present embodiment may include a primary heating step of heating the light ink composition and the dark ink composition adhered to the recording medium. The surface temperature of the recording medium in the primary heating step is preferably 45°C or lower, preferably 28 to 45°C, more preferably 30 to 45°C, still more preferably 32 to 45°C, and particularly preferably 35 to 43°C.

[0172] The primary heating step is a step of heating and drying the light ink composition and the dark ink composition adhered to the recording medium at an early stage. The primary heating step is a heating step for drying at least a part of the solvent component of the ink so as to reduce at least the flow of the ink of the light ink composition and the dark ink composition adhered to the recording medium. By performing such a primary heating step, a pinning effect may be obtained and the image quality tends to be improved. However, when the heating temperature in the primary heating step is high, there are drawbacks such as deterioration of clogging recovery and landing deviation. On the other hand, according to the recording method according to the present embodiment, since an ink set including a light ink composition in which a pinning effect is easily obtained is used, the ink thickens greatly even in heating and drying at a relatively low temperature such as the above preferable temperature range, and both excellent image quality and excellent reduction of landing deviation can be achieved.

[0173] In the primary heating step, the light ink composition and the dark ink composition may be adhered to the heated recording medium, or may be heated at an early stage after adhesion. In the primary heating step, it is preferable that heating is started within 0.5 seconds at the latest from the landing of the ink droplets of the light ink composition and / or the dark ink composition landed on the recording medium.

[0174] The primary heating step is preferably by an IR heater, microwave radiation, a platen heater, or blowing warm air onto the recording medium by a fan.

[0175] The heating in the primary heating step may be performed at least either before, simultaneously with, or shortly after the above-described ink adhesion step, and is preferably performed simultaneously. With such a heating sequence, the ink adhesion step can be performed. Note that the heating temperature in the primary heating step is the surface temperature of the recording medium at the time of ink adhesion when ink is adhered to the heated recording medium, and is the surface temperature of the recording medium at the time of heating when heating is performed shortly after ink adhesion. It is also the maximum temperature during the primary heating step during heating.

[0176] 2.4 Post-heating step The recording method according to this embodiment preferably includes a post-heating step of heating the recording medium to which the light ink composition and the dark ink composition are adhered. Thereby, the drying property is further improved, and there is a tendency to obtain a recording having more excellent rubbing resistance, which is preferable.

[0177] The post-heating step is a heating step that completes the recording and sufficiently heats the recording to a degree that the recording can be used. The post-heating step is a heating step for sufficiently drying the solvent component of the ink and heating a resin or the like that may be contained in the ink to flatten the ink coating film. The post-heating step is preferably started more than 0.5 seconds after the light ink composition and / or the dark ink composition has adhered to the recording medium. For example, it is preferable to start heating the recording area more than 0.5 seconds after all the ink adhesion to a certain recording area of the recording medium is completed. Also, the preferable temperature in the above-described primary heating step and the preferable temperature in the post-heating step are preferably different.

[0178] In the post-heating step, heating of the recording medium can be performed using appropriate heating means, for example, when using an inkjet recording apparatus. Further, it can be performed not only by the heating means provided in the inkjet recording apparatus but also by appropriate heating means. In this case, the surface temperature of the recording medium is preferably 60°C or higher, more preferably 70°C or higher, still more preferably 80°C or higher, and particularly preferably 85°C or higher. Also, the surface temperature of the recording medium heated in the post-heating step is preferably 120°C or lower, more preferably 110°C or lower, still more preferably 100°C or lower, and particularly preferably 95°C or lower.

[0179] 2.5 Other steps The recording method according to this embodiment may include a cleaning step of discharging the ink composition or the processing liquid by means other than the pressure generating means for discharging the ink for recording, that is, taking the inkjet head 2 as shown in FIG. 1 as an example, by another mechanism that is not the mechanism for discharging the ink for recording provided in the inkjet head 2. Examples of the mechanism for discharging the ink for recording provided in the inkjet head 2 include a piezo element and a heater element provided in a pressure chamber (not shown) for applying pressure to the ink.

[0180] This cleaning step may be a step of applying pressure from the outside to the inkjet head 2 to discharge the ink composition or the processing liquid from the nozzles. By providing this step, even when there is a concern that resin or the like adheres to the inner wall of the inkjet head 2, this can be suppressed, and in some cases, the ejection stability can be made even better.

[0181] Note that, as the other mechanisms described above, there are mechanisms for applying pressure such as applying negative pressure (suction) and applying positive pressure from the upstream of the inkjet head. These are not ink discharges (flushing) by the function of the inkjet head itself. That is, at the time of recording, it is not a discharge using the function of discharging ink from the inkjet head.

[0182] 2.6 Inkjet recording apparatus An example of an inkjet recording apparatus that can be suitably used for implementing each step in the recording method according to the present embodiment will be described with reference to the drawings.

[0183] <Schematic of device configuration> FIG. 1 is a schematic cross-sectional view schematically showing an inkjet recording apparatus. FIG. 2 is a perspective view showing an example of the configuration around the carriage of the inkjet recording apparatus 1 in FIG. 1. As shown in FIGS. 1 and 2, the inkjet recording apparatus 1 includes an inkjet head 2, an IR heater 3, a platen heater 4, a heating heater 5, a cooling fan 6, a preheater 7, a ventilation fan 8, a carriage 9, a platen 11, a carriage moving mechanism 13, a conveying means 14, and a control unit CONT. The operation of the entire inkjet recording apparatus 1 is controlled by the control unit CONT shown in FIG. 2.

[0184] <Configuration related to the inkjet head> The inkjet head 2 is configured to perform recording on the recording medium M by ejecting and attaching an ink composition (hereinafter also referred to as "ink") from the nozzles of the inkjet head 2. The same can be applied to the processing liquid. As shown in FIGS. 1 and 2, the inkjet head 2 is a serial type inkjet head, and scans the recording medium M a plurality of times in the main scanning direction relatively to attach ink or a processing liquid to the recording medium M. The inkjet head 2 is mounted on a carriage 9 shown in FIG. 2. The inkjet head 2 is scanned a plurality of times in the main scanning direction relatively to the recording medium M by the operation of a carriage moving mechanism 13 that moves the carriage 9 in the medium width direction of the recording medium M. The medium width direction is the main scanning direction of the inkjet head 2. Scanning in the main scanning direction is also referred to as main scanning.

[0185] Here, the main scanning direction is the direction in which the carriage 9 on which the inkjet head 2 is mounted moves. In FIG. 1, it is a direction intersecting the sub-scanning direction, which is the conveyance direction of the recording medium M indicated by the arrow SS. In FIG. 2, the width direction of the recording medium M, that is, the direction represented by S1 - S2 is the main scanning direction MS, and the direction represented by T1 → T2 is the sub-scanning direction SS. Note that in one scan, scanning is performed in the main scanning direction, that is, either the direction of arrow S1 or arrow S2. Then, by repeatedly performing the main scanning of the inkjet head 2 and the sub-scanning which is the conveyance of the recording medium M a plurality of times, recording is performed on the recording medium M.

[0186] The cartridge 12 that supplies ink or a processing liquid to the inkjet head 2 includes a plurality of independent cartridges. The cartridge 12 is detachably attached to the carriage 9 on which the inkjet head 2 is mounted. Each of the plurality of cartridges can be filled with a different type of ink composition or processing liquid, and the ink composition or processing liquid is supplied from the cartridge 12 to each nozzle. Note that in FIGS. 1 and 2, an example where the cartridge 12 is attached to the carriage 9 is shown, but it is not limited thereto, and it may be provided at a location other than the carriage 9 and supplied to each nozzle by a supply pipe (not shown).

[0187] For the ejection of the inkjet head 2, a conventionally known method can be used. Here, a method of ejecting droplets by utilizing the vibration of a piezoelectric element, that is, an ejection method of forming ink droplets or the like by the mechanical deformation of an electrostrictive element is used.

[0188] <Primary heating mechanism> The inkjet recording apparatus 1 can be provided with a primary heating mechanism for heating the recording medium M when ejecting ink from the inkjet head 2 and attaching it to the recording medium. As the primary heating mechanism, a conduction type, a blowing type, a radiation type, etc. can be used. The conduction type conducts heat from a member in contact with the recording medium to the recording medium. For example, a platen heater or the like can be cited. The blowing type blows normal temperature air or warm air onto the recording medium to dry the ink. For example, a blowing fan can be cited. The radiation type radiates radiation that generates heat onto the recording medium to heat the recording medium. For example, IR radiation can be cited. Also, although not shown, a heater similar to the platen heater may be provided immediately downstream of the platen heater 4 in the SS direction. These primary heating mechanisms may be used alone or in combination. For example, as the primary heating mechanism, an IR heater 3 and a platen heater 4 are provided.

[0189] When the IR heater 3 is used, the recording medium M can be heated in a radiation manner by the radiation of infrared rays from the inkjet head 2 side. As a result, the inkjet head 2 is also likely to be heated at the same time, but it can be heated without being affected by the thickness of the recording medium M compared to the case of heating from the back surface of the recording medium M such as the platen heater 4. In addition, various fans (for example, a ventilation fan 8) for drying the ink on the recording medium M by blowing warm air or air at the same temperature as the environment onto the recording medium M may be provided.

[0190] The platen heater 4 can heat the recording medium M through the platen 11 at a position facing the inkjet head 2. The platen heater 4 is capable of heating the recording medium M in a conduction manner and is used as needed in the inkjet recording method.

[0191] Further, the inkjet recording apparatus 1 may include a preheater 7 that preheats the recording medium M before ink adheres to the recording medium M.

[0192] <Post-heating mechanism> After the ink adhesion step, a post-heating mechanism may be provided that completes the recording and sufficiently heats the recording to a degree where the recorded matter can be used.

[0193] The heating heater 5 used in the post-heating mechanism dries and solidifies the ink adhering to the recording medium M. By heating the recording medium M on which the image is recorded by the heating heater 5, moisture and the like contained in the ink evaporate and disperse more quickly, and an ink film is formed by the resin dispersion that may be contained in the ink. In this way, the ink film firmly adheres or adheres on the recording medium M, resulting in excellent film-forming properties, and an excellent high-quality image can be obtained in a short time.

[0194] <Other configurations> The inkjet recording apparatus 1 may have a cooling fan 6. After drying the ink recorded on the recording medium M, the cooling fan 6 cools the ink on the recording medium M, so that an ink coating film with good adhesion can be formed on the recording medium M.

[0195] Below the carriage 9, a platen 11 that supports the recording medium M, a carriage moving mechanism 13 that relatively moves the carriage 9 with respect to the recording medium M, and a conveying means 14 that is a roller for conveying the recording medium M in the sub-scanning direction are provided. The operations of the carriage moving mechanism 13 and the conveying means 14 are controlled by the control unit CONT.

[0196] <Electrical control> Figure 3 is a functional block diagram of the inkjet recording apparatus 1. The control unit CONT is a control unit for controlling the inkjet recording apparatus 1. The interface unit 101 (I / F) is for transmitting and receiving data between the computer 130 (COMP) and the inkjet recording apparatus 1. The CPU 102 is an arithmetic processing unit for controlling the entire inkjet recording apparatus 1. The memory 103 (MEM) is for securing an area for storing the program of the CPU 102 and a working area, etc. The CPU 102 controls each unit by the unit control circuit 104 (UCTRL). Note that the detector group 121 (DS) monitors the situation inside the inkjet recording apparatus 1, and based on the detection result, the control unit CONT controls each unit.

[0197] The conveyance unit 111 (CONVU) controls the sub-scanning (conveyance) of inkjet recording. Specifically, it controls the conveyance direction and conveyance speed of the recording medium M. More specifically, it controls the conveyance direction and conveyance speed of the recording medium M by controlling the rotation direction and rotation speed of the conveyance roller driven by a motor.

[0198] The carriage unit 112 (CARU) controls the main scanning (pass) of inkjet recording. Specifically, it reciprocates the inkjet head 2 in the main scanning direction. The carriage unit 112 includes a carriage 9 on which the inkjet head 2 is mounted and a carriage moving mechanism 13 for reciprocating the carriage 9.

[0199] The head unit 113 (HU) controls the discharge amount of ink and processing liquid from the nozzles of the inkjet head 2. For example, when the nozzles of the inkjet head 2 are driven by piezoelectric elements, it controls the operation of the piezoelectric elements at each nozzle. The head unit 113 controls the timing of adhesion of each ink and processing liquid, the dot size of the ink and processing liquid, etc. Also, the combination of the control of the carriage unit 112 and the head unit 113 controls the adhesion amount of ink and processing liquid per scan.

[0200] The drying unit 114 (DU) controls the temperatures of various heaters such as the IR heater 3, the preheater 7, the platen heater 4, and the heating heater 5.

[0201] The inkjet recording apparatus 1 alternately repeats the operation of moving the carriage 9 mounting the inkjet head 2 in the main scanning direction and the conveying operation (sub-scanning). At this time, when performing each pass, the control unit CONT controls the carriage unit 112 to move the inkjet head 2 in the main scanning direction, and controls the head unit 113 to discharge droplets of ink or processing liquid from predetermined nozzle holes of the inkjet head 2, and attaches the droplets of ink or processing liquid to the recording medium M. Further, the control unit CONT controls the conveyance unit 111 to convey the recording medium M in the conveyance direction at a predetermined conveyance amount (feed amount) during the conveyance operation.

[0202] In the inkjet recording apparatus 1, by repeating the main scanning (pass) and the sub-scanning (conveying operation), the recording area to which a plurality of droplets are attached is gradually conveyed. Then, the ink attached to the recording medium M is dried by the heating heater 5, and the image is completed. Thereafter, the completed recording may be wound up in a roll shape by a winding mechanism or conveyed by a flatbed mechanism. In addition to the serial type inkjet recording apparatus as described above, a line type inkjet recording apparatus can also be used for recording.

[0203] 3. Examples Hereinafter, the present invention will be described more specifically by way of examples, but the present invention is not limited to these examples. Hereinafter, “%” is based on mass unless otherwise specified.

[0204] 3.1 Preparation of Light Ink Composition and Dark Ink Composition Each component was placed in a container so as to have the compositions shown in Tables 1 to 3 below, mixed and stirred with a magnetic stirrer for 2 hours, and then filtered through a membrane filter with a pore size of 5 μm, thereby obtaining the light ink compositions and the concentrated ink compositions according to Examples and Comparative Examples. All the numerical values in Tables 1 to 3 below indicate mass %, and pure water was added so that the total mass of the ink composition was 100 mass %. In addition, a pigment dispersion prepared in advance as described below was used. The numerical values in the table for the pigment dispersion and the water-dispersible resin indicate the amount of their active ingredients (in terms of solid content).

[0205] [Preparation of Pigment Dispersion] 50 g of methyl ethyl ketone (MEK) was added to a flask equipped with a dropping funnel, a nitrogen introduction tube, a reflux condenser, a thermometer, and a stirring device, and heated to 75 °C while bubbling nitrogen. A mixture of 80 g of butyl methacrylate, 50 g of methyl methacrylate, 15 g of styrene, 20 g of methacrylic acid, 50 g of MEK, and 500 mg of a polymerization initiator (azobisisobutyronitrile / AIBN) was added dropwise from the dropping funnel over 3 hours. After the dropwise addition, the mixture was further heated under reflux for 6 hours, and after cooling, MEK in the evaporated portion was added to obtain a resin solution (resin solid content: 50 mass %, acid value: 79 mg / KOH, Tg: 65 °C). A predetermined amount of a 20 mass % aqueous sodium hydroxide solution was added to 20 g of the solution as a neutralizing agent to neutralize 100% of the salt-forming groups. While stirring, 50 g of a pigment (C.I. Pigment Blue 15:3) was gradually added thereto, and then kneaded with a bead mill for 2 hours. 200 g of ion-exchanged water was added to the obtained kneaded product, stirred, and then heated under reduced pressure to distill off MEK. Further, the concentration was adjusted with ion-exchanged water to obtain a pigment dispersion (pigment solid content: 20 mass %, resin solid content: 5 mass %).

[0206] 3.2 Preparation of Treatment Liquid The respective components were placed in a container so as to have the composition shown in Table 4 below, mixed and stirred with a magnetic stirrer for 2 hours, and then filtered through a membrane filter with a pore size of 5 μm to obtain the treatment liquids according to the examples and comparative examples. All of the numerical values in Table 4 below indicate mass%, and pure water was added so that the total mass of the treatment liquid was 100 mass%. Note that the numerical values in the table for the cationic resin indicate the amount of its active ingredient (in terms of solid content).

[0207]

Table 1

[0208]

Table 2

[0209]

Table 3

[0210]

Table 4

[0211] Supplementary explanations are provided for the descriptions in Tables 1 to 4 above. <Terms> “Specific alkane diol condensate”: A condensate of an alkane diol having 2 or 3 carbon atoms and having two hydroxyl groups, which is an organic solvent “Specific alkane diol monomer”: An alkane diol having 2 to 4 carbon atoms, which is an organic solvent “C3 condensate”: An intermolecular condensate of an alkane diol having 3 carbon atoms “C2 condensate”: An intermolecular condensate of an alkane diol having 2 carbon atoms “Boiling point”: Indicates the standard boiling point

[0212] <Components> (Specific alkane diol condensate) “DPG”: Dipropylene glycol “DEG”: Diethylene glycol "TEG": Triethylene glycol "TPG": Tripropylene glycol (Specific alkanediol monomers) "PG": Propylene glycol "EG": Ethylene glycol "1,3PD": 1,3 - Propanediol (Other alkanediols) "1,2HD": 1,2 - Hexanediol (Other organic solvents) "2P": 2 - Pyrrolidone "DMSO": Dimethyl sulfoxide "EOXM": 3 - Ethyl - 3 - oxetanemethanol (Alkanolamines) "TIPA": Triisopropanolamine, standard boiling point 301 °C. Solid at room temperature. (Pigment dispersion) "Cyan pigment": C.I. Pigment Blue 15:3 (Water - dispersible resin) "Joncryl 631": Resin emulsion, styrene - acrylic resin, trade name of BASF Japan Ltd., Tg(105 °C) "Hi - Tech E - 6500": Wax emulsion, polyethylene - based wax, trade name of Toho Chemical Industry Co., Ltd. (Surfactant) "BYK - 333": Silicone - based surfactant, trade name of BYK - Chemie Japan Ltd. "Surfynol DF110D": Acetylenediol - based surfactant, trade name of Nissin Chemical Industry Co., Ltd. (Flocculant) "Cation Master PD - 7": Amine - epichlorohydrin copolymer, trade name of Yokkaichi Gosei Co., Ltd.

[0213] 3.3 Printing conditions The printing conditions in the evaluation test were as follows. [Printing conditions] Printer: "SC - R5050", trade name of Seiko Epson Corporation Resolution: 1200×1200 dpi Coating amount: Concentrated ink composition (10 mg / inch 2 ), Light ink composition (5 mg / inch 2 ), Treatment liquid (1 mg / inch 2 ) Printing pattern: Solid pattern (cyan, light cyan mixed color) Scanning times: 9 times Platen heating temperature: 40°C Post-heating temperature: 80°C Recording medium: "Orajet 3165G-010", product name manufactured by Orafol Japan Co., Ltd., vinyl chloride film Platen gap: 1.7 mm

[0214] The concentrated ink composition, light ink composition, and treatment liquid obtained above were filled into "SC-R5050", the recording medium was set, and a solid pattern of light and dark mixing was printed under the above printing conditions. In the test of Comparative Example 3, the treatment liquid was not used. Under the above printing conditions, the adhesion amount ratio of the concentrated ink composition to the light ink composition is (concentrated ink composition: light ink composition) = (2:1). The platen heating temperature indicates the surface temperature of the recording medium in the primary heating process. Similarly, the post-heating temperature indicates the surface temperature of the recording medium in the post-heating process.

[0215]

Table 5

[0216] 3.4 Evaluation method As evaluation items, evaluation tests were conducted on image quality (aggregation unevenness), landing deviation, abrasion resistance, and clogging recovery. The evaluation method is as follows.

[0217] 3.4.1 Image quality (aggregation unevenness) The recording medium was set, a solid pattern of light and dark mixing was printed under the above printing conditions, the printed matter was visually observed, and the determination was made according to the following evaluation criteria. 〔Evaluation criteria〕 AA: No aggregation unevenness A: There is aggregation unevenness, but it is not a concern. B: Aggregation unevenness is noticeable but acceptable. C: Aggregation unevenness is prominent (NG).

[0218] 3.4.2 Landing deviation Under the above printing conditions, the recording medium was set, and immediately after flushing, a nozzle check pattern was recorded to confirm normal ejection. Then, with the temperature of the platen at 40 °C, the ink was not ejected and an idle run was performed for 20 seconds, and the same nozzle check pattern was recorded. The landing deviation of the light and dark inks after the idle run operation was compared and judged according to the following evaluation criteria. Note that the landing deviation was taken as the average value for all nozzles, excluding non-ejecting nozzles. Before the idle run, the ejection timing between the light and dark inks was adjusted so that there was no deviation in the landing position, and it was performed under that ejection timing condition. 〔Evaluation criteria〕 AA: There is no difference in the landing position between the light and dark inks. A: There is a deviation within half of the nozzle pitch between the light and dark inks. B: There is a deviation within the nozzle pitch between the light and dark inks. C: There is a deviation exceeding the nozzle pitch between the light and dark inks.

[0219] 3.4.3 Rub resistance After printing a solid pattern on the recording medium under the above printing conditions, it was left at room temperature for 30 minutes. The solid pattern printed area was cut into a 30×150 mm rectangle, and the degree of ink peeling when rubbed 100 times with a Kagaku-shinbunshi rubbing tester (load 500 g) using plain woven fabric was visually evaluated. 〔Evaluation criteria〕 AA: No peeling A: There is peeling less than 20% of the evaluation area. B: There is peeling less than 50% of the evaluation area. C: There is peeling 50% or more of the evaluation area.

[0220] 3.4.4 Clogging recovery Under the above printing conditions, non-ejection was intentionally caused in the nozzles. In this state, the printer was run idle for 3 hours under the temperature conditions described in the above printing conditions. After recording, cleaning was performed 3 times, and finally, the number of nozzles that had fallen out was determined according to the following evaluation criteria. For each cleaning, 0.5 g of ink was discharged from the nozzle array. Note that non-ejection of the nozzles was caused by tapping the nozzle surface with a wet bench cot. The nozzle array consists of 400 nozzles. 〔Evaluation Criteria〕 AA: No nozzle non-ejection A: Less than 3% nozzle non-ejection B: 3% or more and less than 5% nozzle non-ejection C: 5% or more nozzle non-ejection

[0221] 3.5 Evaluation Results The evaluation results are shown in Table 5 and Tables 1 - 2 above.

[0222] From the comparison of each example and each comparative example, it can be seen that in the examples, the ink set and the recording method according to the present embodiment can all obtain excellent image quality and can excellently reduce landing deviation. On the other hand, all the comparative examples that are not in the present embodiment are inferior in either image quality or reduction of landing deviation.

[0223] From the comparison between Example 1 and Comparative Examples 1 - 2, it can be seen that by containing a specific condensate in the light ink composition and a specific monomer in the concentrated ink composition, excellent image quality can be obtained and landing deviation can be excellently reduced. In addition, from the comparison between Example 1 and Comparative Example 3, it can be seen that a treatment liquid containing a flocculant is necessary to obtain excellent image quality.

[0224] From the results of Examples 1, 2 - 3, it can be seen that when the specific monomer that can be contained in the light ink composition is propylene glycol, the abrasion resistance is more excellent.

[0225] From the results of Examples 1, 4 - 5, it can be seen that when the content of the organic solvent having a standard boiling point exceeding 250°C does not exceed a predetermined amount, the abrasion resistance is more excellent.

[0226] From the results of Examples 1 and 6, it can be seen that when the light ink composition can contain a specific monomer, the content of the specific condensate being less than the content of the specific monomer can result in excellent balance among image quality, landing deviation, and abrasion resistance.

[0227] From the results of Examples 1 and 7, it can be seen that when the light ink composition can contain alkanolamines, having a higher content of alkanolamines in the light ink composition than in the dark ink composition can result in excellent balance between image quality and landing deviation. Also, from the results of Examples 1 and 14, it can be seen that the image quality is better when the ink composition contains alkanolamines.

[0228] From the results of Examples 1, 9, and 10, it can be seen that when a low-molecular organic compound can be included, a low-molecular organic compound composed of amides results in better abrasion resistance and clogging recovery properties.

[0229] From the results of Examples 1, 11, and 12, it can be seen that when the light ink composition contains a specific monomer, the image quality, landing deviation, and abrasion resistance can be well balanced.

[0230] From the results of Examples 1, 8, and 13, it can be seen that when the content of the organic solvent having a standard boiling point of 250°C or lower is below a predetermined amount, the image quality, landing deviation, and abrasion resistance can be well balanced.

[0231] From the results of Examples 1 and 15, it can be seen that the image quality, landing deviation, and abrasion resistance can be well balanced when the dark ink composition does not contain a specific condensate.

[0232] From the results of Examples 1, 16, and 17, it can be seen that various types of flocculants can be applied to the treatment liquid.

[0233] The following content is derived from the above-described embodiments.

[0234] One aspect of the ink set is a treatment liquid containing a flocculant, and a concentrated ink composition and a light ink composition, which contain coloring materials, are of the same color system, and are water-based inkjet inks. The light ink composition contains an organic solvent that is a condensate of an alkanediol having 2 or 3 carbon atoms and has 2 hydroxyl groups. The concentrated ink composition contains an organic solvent that is an alkanediol having 2 to 4 carbon atoms.

[0235] In one aspect of the above ink set, the light ink composition may further contain an organic solvent that is an alkanediol having 2 to 4 carbon atoms, and the content of the organic solvent that is a condensate of an alkanediol having 2 or 3 carbon atoms and has 2 hydroxyl groups may be less than the content of the organic solvent that is an alkanediol having 2 to 4 carbon atoms.

[0236] In any aspect of the above ink set, the organic solvent that is a condensate of an alkanediol having 2 or 3 carbon atoms and has 2 hydroxyl groups contained in the light ink composition and the organic solvent that is an alkanediol having 2 to 4 carbon atoms contained in the concentrated ink composition may each have a standard boiling point of 150 to 300 °C.

[0237] In any aspect of the above ink set, the light ink composition may contain an organic solvent that is an alkanediol having 2 to 4 carbon atoms without exceeding the content of the organic solvent that is an alkanediol having 2 to 4 carbon atoms in the concentrated ink composition.

[0238] In any aspect of the above ink set, the concentrated ink composition may contain an organic solvent that is a condensate of an alkanediol having 2 or 3 carbon atoms and has 2 hydroxyl groups without exceeding the content of the organic solvent that is a condensate of an alkanediol having 2 or 3 carbon atoms and has 2 hydroxyl groups in the light ink composition.

[0239] In any aspect of the above ink set, the concentrated ink composition and the light ink composition each contain alkanolamines, and the content of the alkanolamines in the light ink composition may be higher than that in the concentrated ink composition.

[0240] In any aspect of the above ink set, the concentrated ink composition and the light ink composition each contain an organic solvent having a standard boiling point of 250°C or lower in an amount of 10 to 30% by mass based on the total mass of the composition, and do not contain an organic solvent having a standard boiling point exceeding 250°C in an amount exceeding 8% by mass based on the total mass of the composition.

[0241] In any aspect of the above ink set, the concentrated ink composition and the light ink composition may each contain a low-molecular organic compound having a standard boiling point of 150 to 300°C and being any one of amides, sulfur-containing compounds, and cyclic ethers.

[0242] In any aspect of the above ink set, the concentrated ink composition and the light ink composition may each contain a resin dispersion composed of any one of an acrylic resin, a polyurethane resin, a polyester resin, and a polyolefin resin.

[0243] In any aspect of the above ink set, It may be used for recording on a low-absorbency recording medium or a non-absorbency recording medium.

[0244] One aspect of the recording method is In a recording method using the ink set of any of the above aspects, it includes a step of attaching the treatment liquid to a recording medium and a step of attaching the light ink composition and the concentrated ink composition to the recording medium by an inkjet method.

[0245] In one aspect of the above recording method, a primary heating step of heating the light ink composition and the dark ink composition adhered to the recording medium is provided, and the surface temperature of the recording medium in the primary heating step may be 28 to 45°C.

[0246] The present invention is not limited to the above-described embodiments, and various modifications are possible. For example, the present invention includes configurations that are substantially the same as the configurations described in the embodiments, for example, configurations having the same functions, methods, and results, or configurations having the same objectives and effects. In addition, the present invention includes configurations in which non-essential parts of the configurations described in the embodiments are replaced. Further, the present invention includes configurations that exhibit the same operational effects as the configurations described in the embodiments or configurations that can achieve the same objectives. In addition, the present invention includes configurations in which known technologies are added to the configurations described in the embodiments.

Explanation of Reference Numerals

[0247] 1... Inkjet recording apparatus, 2... Inkjet head, 3... IR heater, 4... Platen heater, 5... Heating heater, 6... Cooling fan, 7... Preheater, 8... Ventilation fan, 9... Carriage, 11... Platen, 12... Cartridge, 13... Carriage movement mechanism, 14... Conveying means, 101... Interface unit, 102... CPU, 103... Memory, 104... Unit control circuit, 111... Conveying unit, 112... Carriage unit, 113... Head unit, 114... Drying unit, 121... Detector group, 130... Computer, CONT... Control unit, MS... Main scanning direction, SS... Sub-scanning direction, M... Recording medium

Claims

1. A treatment liquid containing a flocculant, a concentrated ink composition and a light ink composition, which contain a coloring material, are of the same color system, and are water-based inkjet inks, and are used for recording on a recording medium that is a low-absorbency recording medium or a non-absorbency recording medium, wherein, the light ink composition contains an organic solvent that is a condensate of an alkanediol having 2 or 3 carbon atoms and has 2 hydroxyl groups, the concentrated ink composition contains an organic solvent that is an alkanediol having 2 to 4 carbon atoms, the content of the organic solvent that is a condensate of an alkanediol having 2 or 3 carbon atoms and has 2 hydroxyl groups in the concentrated ink composition is 2.0% by mass or less based on the total mass of the concentrated ink composition, the content of the organic solvent that is a condensate of an alkanediol having 2 or 3 carbon atoms and has 2 hydroxyl groups in the concentrated ink composition is less than the content of the organic solvent that is a condensate of an alkanediol having 2 or 3 carbon atoms and has 2 hydroxyl groups in the light ink composition, the content of the organic solvent that is an alkanediol having 2 to 4 carbon atoms in the concentrated ink composition is equal to or more than the content of the organic solvent that is an alkanediol having 2 to 4 carbon atoms in the light ink composition, an ink set.

2. The light ink composition further contains an organic solvent that is an alkanediol having 2 to 4 carbon atoms, and the content of the organic solvent that is a condensate of an alkanediol having 2 or 3 carbon atoms and has 2 hydroxyl groups is less than the content of the organic solvent that is an alkanediol having 2 to 4 carbon atoms, the ink set according to claim 1.

3. The organic solvent that is a condensate of an alkanediol having 2 or 3 carbon atoms and has 2 hydroxyl groups contained in the light ink composition and the organic solvent that is an alkanediol having 2 to 4 carbon atoms contained in the concentrated ink composition each have a standard boiling point of 150 to 300°C, the ink set according to claim 1 or claim 2.

4. The content of the organic solvent that is an alkanediol having 2 to 4 carbon atoms in the light ink composition is 20% by mass or less based on the total mass of the light ink composition described above, the ink set according to any one of claims 1 to 3.

5. The content of the organic solvent that is a condensate of an alkanediol having 2 or 3 carbon atoms and has 2 hydroxyl groups in the concentrated ink composition is 0 to 1.0% by mass based on the total mass of the concentrated ink composition, the ink set according to any one of claims 1 to 4.

6. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ The concentrated ink composition and the light ink composition each contain alkanolamines. The light ink composition contains a larger amount of the alkanolamines than the concentrated ink composition. The ink set according to any one of claims 1 to 5.

7. The concentrated ink composition and the light ink composition each contain an organic solvent having a standard boiling point of 250 ° C or lower in an amount of 10 to 30% by mass based on the total mass of the composition, and do not contain an organic solvent having a standard boiling point exceeding 250 ° C in an amount exceeding 8% by mass based on the total mass of the composition. The ink set according to any one of claims 1 to 6.

8. The concentrated ink composition and the light ink composition each contain a low molecular organic compound having a standard boiling point of 150 to 300 ° C and being any one of amides, sulfur-containing compounds, and cyclic ethers. The ink set according to any one of claims 1 to 7.

9. The concentrated ink composition and the light ink composition each contain a resin dispersion composed of any one of an acrylic resin, a polyurethane resin, a polyester resin, and a polyolefin resin. The ink set according to any one of claims 1 to 8.

10. The low-absorbency recording medium is a low-absorbency recording medium provided with a coating layer on the surface, and the non-absorbent recording medium has a recording surface made of plastic. The ink set according to any one of claims 1 to 9.

11. The flocculant contains either a polyvalent metal salt or an organic acid. The ink set according to any one of claims 1 to 10.

12. In the recording method using the ink set according to any one of claims 1 to 11, a step of attaching the treatment liquid to a recording medium, and a step of attaching the light ink composition and the concentrated ink composition to the recording medium by an inkjet method, wherein the recording medium is a low-absorbency recording medium or a non-absorbent recording medium. Recording method.

13. A primary heating step of heating the light ink composition and the concentrated ink composition attached to the recording medium is provided, and the surface temperature of the recording medium in the primary heating step is 28 to 45 ° C. The recording method according to claim 12. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

Images