JP7634156B2 - Ink set, image forming method, and image forming apparatus - Google Patents

Description

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

Inks using coloring materials such as pigments are known for use in applications requiring water resistance and light resistance, such as posters. When such inks are ejected by inkjet recording onto a low-absorbency recording medium, such as coated paper used in commercial printing, adjacent droplets coalesce on the recording medium, causing image defects (beading). A known method for eliminating this type of beading is to apply a treatment liquid containing a polyvalent metal salt that acts to aggregate the coloring materials in the ink to the recording medium before ejecting the ink.

Patent Document 1 discloses a treatment liquid for inkjet recording that contains water, glycerin, and at least one polyvalent metal salt selected from the group consisting of calcium nitrate and magnesium nitrate, in which the content of glycerin in the treatment liquid is 10% by mass to 50% by mass, and the content of the polyvalent metal salt in the treatment liquid is 0.8 mol/L to 2.0 mol/L.

However, when applying ink to the areas of the recording medium to which the pretreatment liquid has been applied after applying the pretreatment liquid to the recording medium, there is a problem that the glossiness of the image formed by the ink decreases and that the abrasion resistance decreases.

The present invention relates to an ink set having a pretreatment liquid to be applied to a recording medium, and an ink to be applied to an area of the recording medium to which the pretreatment liquid has been applied, wherein the pretreatment liquid contains a polyvalent metal salt, water, an organic solvent, and a compound represented by the following general formula (1); the ink contains a colorant, water, an organic solvent, and a compound represented by the following general formula (1); and the compound represented by the general formula (1) contained in the pretreatment liquid has a degree of saponification of 63 or more and 100 or less, and a degree of polymerization of 100 or more and 270 or less.
(In the above general formula (1), m and n each independently represent an integer.)

According to the present invention, it is possible to provide an ink set that suppresses a decrease in gloss and abrasion resistance of an image formed with ink when a pretreatment liquid is applied to a recording medium and then ink is applied to the area of the recording medium to which the pretreatment liquid has been applied.

FIG. 1 is a schematic diagram showing an example of an image forming apparatus.

One embodiment of the present invention is described below.

<<Ink set>>
The ink set of the present disclosure preferably includes a pretreatment liquid and an ink, and further includes other components as necessary. The ink set may include one or more pretreatment liquids and inks.
In the present disclosure, an "ink set" may refer to a set in which the pretreatment liquid and the ink exist in an independent state, and is not limited to a set in which, for example, a pretreatment liquid storage means that stores the pretreatment liquid and an ink storage means that stores the ink are manufactured, sold, etc. in an integrated state. For example, even if the pretreatment liquid storage means and the ink storage means are manufactured, sold, etc. independently, the set is included in a set in cases where it is assumed that the pretreatment liquid and the ink will be used in combination, or where it substantially induces the pretreatment liquid and the ink to be used in combination.
The "pretreatment liquid" in this disclosure is a liquid composition that is applied to a recording medium and causes aggregation or thickening in the ink upon contact with the ink that is subsequently applied to the area where the pretreatment liquid has been applied.
In this disclosure, the term "ink" refers to a liquid composition that forms an image by being applied to an area of a recording medium to which the pretreatment liquid has been applied.

<Pretreatment solution>
The pretreatment liquid contains a compound represented by general formula (1), a polyvalent metal salt, water, and an organic solvent, and optionally contains a compound represented by general formula (2), a surfactant, and other components.

-Compound represented by general formula (1) (polyvinyl alcohol)-
The pretreatment liquid contains a compound represented by the following general formula (1), having a degree of saponification of 63 to 100 and a degree of polymerization of 100 to 270. The compound represented by general formula (1) contained in the pretreatment liquid suppresses a decrease in gloss and a decrease in abrasion resistance of an image formed by ink applied to an area to which the pretreatment liquid is applied. In the present disclosure, the degree of saponification is represented by "{m/(m+n)}×100", and the degree of polymerization is represented by "m+n". The compound represented by general formula (1) is also referred to as polyvinyl alcohol.
(In the above general formula (1), m and n each independently represent an integer.)

First, the reason why the decrease in gloss and the decrease in abrasion resistance can be suppressed by containing a compound represented by the general formula (1) having a degree of saponification of 63 or more and 100 or less and a degree of polymerization of 100 or more and 270 or less will be described.
Generally, the pretreatment liquid is a liquid composition that causes the coloring material in the ink to aggregate and thicken when it comes into contact with the ink to be applied later, and therefore the coloring material in the ink is less uniformly dispersed when it comes into contact with the pretreatment liquid, which leads to a decrease in uniformity on the surface of the image formed by the ink, resulting in a problem of a decrease in gloss.
Furthermore, in an image formed by using a pretreatment liquid and an ink in combination to aggregate the coloring material in the ink and thicken the ink, the aggregated coloring material (hereinafter also referred to as an aggregate of coloring material) is present on the image surface, which causes a problem of abrasion resistance. This problem tends to become prominent when an image is formed on a recording medium that is a low-permeability substrate such as coated paper, thick paper, or paperboard, or when ink is applied to a recording medium to which a pretreatment liquid has been applied without heating.
In response to these problems, by including in the pretreatment liquid a compound represented by the general formula (1), having a degree of saponification of 63 to 100, and a degree of polymerization of 100 to 270, a component that aggregates the coloring material (hereinafter also referred to as the aggregation component) can be present in a larger amount on the recording medium surface to which the pretreatment liquid is applied, and when the ink and the pretreatment liquid come into contact with each other, a larger amount of the aggregation component can act on the coloring material, and a larger aggregate of the coloring material can be formed. Since the large aggregate of the coloring material is likely to sink in the ink, it is presumed that the image surface will be in a state in which there is more resin than aggregate of the coloring material. As a result, the presence of a large amount of resin on the image surface reduces the unevenness of the image surface, and the decrease in glossiness is suppressed. In addition, the decrease in the unevenness of the image surface reduces the coefficient of friction, and the resin in the pretreatment liquid improves the adhesion of the coloring material to the recording medium, so that the decrease in abrasion resistance is suppressed.

Moreover, it is more preferable that the compound represented by general formula (1) has a degree of saponification of 63 or more and 81 or less, and a degree of polymerization of 100 or more and 270 or less. By having the degree of saponification and the degree of polymerization within this range, the decrease in abrasion resistance can be further suppressed.

The compound represented by the general formula (1) may be appropriately synthesized or may be a commercially available product. Examples of commercially available products include JMR-3HH (manufactured by Nippon Vinyl Acetate & Poval Corporation), JMR-10HH (manufactured by Nippon Vinyl Acetate & Poval Corporation), JMR-3H (manufactured by Nippon Vinyl Acetate & Poval Corporation), JMR-10H (manufactured by Nippon Vinyl Acetate & Poval Corporation), JMR-3M (manufactured by Nippon Vinyl Acetate & Poval Corporation), JMR-8M (manufactured by Nippon Vinyl Acetate & Poval Corporation), and JMR-10M (manufactured by Nippon Vinyl Acetate & Poval Corporation). These may be used alone or in combination of two or more. Among these, JMR-10H (manufactured by Nippon Vinyl Acetate & Poval Corporation), JMR-8M (manufactured by Nippon Vinyl Acetate & Poval Corporation), and JMR-10M (manufactured by Nippon Vinyl Acetate & Poval Corporation) are preferred.

The content of the compound represented by formula (1) is preferably 0.1% by mass or more and 10.0% by mass or less, and more preferably 1.0% by mass or more and 5.0% by mass or less, relative to the mass of the pretreatment liquid. By having the content be 0.1% by mass or more and 10.0% by mass or less, it is possible to further suppress the decrease in glossiness and the decrease in abrasion resistance, and also to apply the pretreatment liquid uniformly to the recording medium.

- Polyvalent metal salts -
The polyvalent metal salt associates with the colorant in the ink due to the charge action, forms an aggregate of the colorant, separates the colorant from the liquid phase, and promotes fixation to the recording medium, thereby suppressing the occurrence of beading in the image formed by the ink, even when a low-permeability substrate is used as the recording medium.

The polyvalent metal salt is not particularly limited and can be appropriately selected according to the purpose, and examples thereof include salts of titanium compounds, chromium compounds, copper compounds, cobalt compounds, strontium compounds, barium compounds, iron compounds, aluminum compounds, calcium compounds, magnesium compounds, zinc compounds, nickel compounds, etc. These may be used alone or in combination of two or more. Among these, salts of calcium compounds, magnesium compounds, and nickel compounds are preferred, and alkaline earth metal salts such as calcium and magnesium are more preferred, from the viewpoint of effectively flocculating coloring materials such as pigments.
The polyvalent metal salt is preferably an ionic salt, and more preferably a magnesium salt or a calcium salt.

The magnesium compound is not particularly limited and can be appropriately selected depending on the purpose. Examples of the magnesium compound include magnesium chloride, magnesium acetate, magnesium sulfate, magnesium nitrate, and magnesium silicate.
The calcium compound is not particularly limited and can be appropriately selected depending on the purpose. Examples of the calcium compound include calcium carbonate, calcium nitrate, calcium chloride, calcium acetate, calcium sulfate, and calcium silicate.
The barium compound is not particularly limited and can be appropriately selected depending on the purpose. For example, barium sulfate is included.
The zinc compound is not particularly limited and can be appropriately selected depending on the purpose. Examples of the zinc compound include zinc sulfide and zinc carbonate.
The aluminum compound is not particularly limited and can be appropriately selected depending on the purpose. Examples of the aluminum compound include aluminum silicate and aluminum hydroxide.
Among these, magnesium nitrate, calcium nitrate, magnesium sulfate, etc. are preferred in view of their solubility in solvents.

The content of the polyvalent metal salt is preferably 0.8 mol/kg or more and 1.4 mol/kg or less based on the total amount of the pretreatment liquid. By having a polyvalent metal salt content of 0.8 mol/kg or more, the occurrence of beading can be suppressed even when a recording medium with low ink absorbency is used, and a high-quality image can be formed. In addition, by having a polyvalent metal salt content of 1.4 mol/kg or less, the storage stability of the pretreatment liquid is improved.

When glycerin is used as the organic solvent described below, the mass ratio of the glycerin content to the polyvalent metal salt content is preferably 1.05 or more, and more preferably 1.2 or more. A mass ratio of 1.05 or more suppresses the precipitation of crystals of the polyvalent metal salt, and can suppress abnormal images (uneven image density) caused by the precipitation of crystals.

-water-
As the water, for example, pure water such as ion-exchanged water, ultrafiltered water, reverse osmosis water, distilled water, or ultrapure water can be used.
The water content is not particularly limited and can be appropriately selected depending on the purpose. From the viewpoint of drying property, the water content is preferably from 10 mass % to 90 mass % and more preferably from 20 mass % to 60 mass % based on the total amount of the contained liquid (pretreatment liquid).

- Organic solvents -
The organic solvent is not particularly limited, and a water-soluble organic solvent can be used. Examples of the water-soluble organic solvent include polyhydric alcohols, ethers such as polyhydric alcohol alkyl ethers and polyhydric alcohol aryl ethers, nitrogen-containing heterocyclic compounds, amides, amines, and sulfur-containing compounds.
Specific examples of the water-soluble organic solvent include ethylene glycol, diethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 3-methyl-1,3-butanediol, triethylene glycol, polyethylene glycol, polypropylene glycol, 1,2-pentanediol, 1,3-pentanediol, 1,4-pentanediol, 2,4-pentanediol, 1,5-pentanediol, and the like. polyhydric alcohols such as pentanediol, 1,2-hexanediol, 1,6-hexanediol, 1,3-hexanediol, 2,5-hexanediol, 1,5-hexanediol, glycerin, 1,2,6-hexanetriol, 2-ethyl-1,3-hexanediol, ethyl-1,2,4-butanetriol, 1,2,3-butanetriol, 2,2,4-trimethyl-1,3-pentanediol, and petriol; ethylene glycol monoethyl ether; and ethylene glycol monobutyl ether. polyhydric alcohol alkyl ethers such as diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, and propylene glycol monoethyl ether; polyhydric alcohol aryl ethers such as ethylene glycol monophenyl ether and ethylene glycol monobenzyl ether; nitrogen-containing heterocyclic compounds such as 2-pyrrolidone, N-methyl-2-pyrrolidone, N-hydroxyethyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, ε-caprolactam, and γ-butyrolactone; amides such as formamide, N-methylformamide, N,N-dimethylformamide, 3-methoxy-N,N-dimethylpropionamide, and 3-butoxy-N,N-dimethylpropionamide; amines such as monoethanolamine, diethanolamine, and triethylamine; sulfur-containing compounds such as dimethyl sulfoxide, sulfolane, and thiodiethanol; propylene carbonate, and ethylene carbonate.
It is preferable to use an organic solvent having a boiling point of 250° C. or less, since this not only functions as a wetting agent but also provides good drying properties.

The content of the organic solvent is preferably 10% by mass or more and 60% by mass or less, and more preferably 20% by mass or more and 60% by mass or less, based on the total amount of the liquid (pretreatment liquid) contained, from the viewpoint of drying property.

-Compound represented by formula (2) (polyoxyethylene alkyl ether)-
The pretreatment liquid may contain a compound represented by the following general formula (2). The compound represented by the general formula (2) is a polyoxyalkylene alkyl ether. By including the compound represented by the general formula (2) in the pretreatment liquid, the pretreatment liquid is more likely to wet and spread when applied to the recording medium. As a result, the pretreatment liquid spreads thinly and uniformly on the surface of the recording medium, shortening the time until the pretreatment liquid applied to the recording medium dries. In addition, the permeability of the pretreatment liquid into the recording medium is improved. As a result, the drying property of the ink applied to the area of the recording medium to which the pretreatment liquid is applied is improved, and the formed image is strengthened and the abrasion resistance is further improved.
(In the above general formula (2), n represents an integer of 3 or more and 11 or less.)

As described above, n in the general formula (2) represents an integer of 3 to 11, and is preferably an integer of 6 to 8. When n is an integer of 3 to 11, the pretreatment liquid is more likely to spread when applied to the recording medium. As a result, the pretreatment liquid spreads thinly and uniformly on the surface of the recording medium, and the time until the pretreatment liquid applied to the recording medium dries is shorter. In addition, the permeability of the pretreatment liquid into the recording medium is also improved. As a result, the drying property of the ink applied to the area of the recording medium to which the pretreatment liquid is applied is improved, the formed image is stronger, and the abrasion resistance is further improved. This effect is remarkable when a high boiling point solvent such as glycerin is used as the organic solvent contained in the pretreatment liquid. In addition, when n is an integer of 6 to 8, the abrasion resistance is further improved by the same effect.

As the compound represented by the general formula (2), a compound appropriately synthesized or a commercially available product may be used. Examples of commercially available products include TRITON HW-1000 (manufactured by Dow Chemical Co.), TERGITOL TMN-3 (manufactured by Dow Chemical Co.), TERGITOL TMN-6 (manufactured by Dow Chemical Co.), TERGITOL TMN-100X (manufactured by Dow Chemical Co.), and TERGITOL TMN-10 (manufactured by Dow Chemical Co.). These may be used alone or in combination of two or more types. Among these, TRITON HW-1000 (manufactured by Dow Chemical Co.) and TERGITOL TMN-6 (manufactured by Dow Chemical Co.) are preferred.

The content of the compound represented by formula (2) is preferably 0.0005% by mass or more and 1.6% by mass or less, and more preferably 0.001% by mass or more and 0.2% by mass or less, relative to the mass of the pretreatment liquid. When the content is 0.0005% by mass or more and 1.6% by mass or less, it is possible to improve abrasion resistance while suppressing the occurrence of beading.

-Surfactants-
The surfactant can improve the wettability of the liquid (pretreatment liquid) contained in the ink to various recording media by lowering the surface tension, so that the ink can be applied evenly. The surfactant can also increase the penetration speed into various recording media by making the liquid contained in the ink moderately wet the recording media. By increasing the penetration speed, excessive aggregation of the coloring material contained in the ink applied to the recording media to which the pretreatment liquid has been applied can be suppressed.

As the surfactant, any of silicone-based surfactants, fluorine-based surfactants, amphoteric surfactants, nonionic surfactants, and anionic surfactants can be used.
The silicone surfactant is not particularly limited and can be appropriately selected according to the purpose. Among them, those that do not decompose even at high pH are preferable. Examples of silicone surfactants include side chain modified polydimethylsiloxane, both end modified polydimethylsiloxane, one end modified polydimethylsiloxane, and both end modified polydimethylsiloxane of side chain. Those having a polyoxyethylene group or a polyoxyethylene polyoxypropylene group as a modified group are particularly preferable because they show good properties as an aqueous surfactant. In addition, polyether modified silicone surfactants can also be used as silicone surfactants, and examples thereof include compounds in which a polyalkylene oxide structure is introduced into the Si part side chain of dimethylsiloxane.
As the fluorine-based surfactant, for example, perfluoroalkyl sulfonic acid compound, perfluoroalkyl carboxylic acid compound, perfluoroalkyl phosphate compound, perfluoroalkyl ethylene oxide adduct and polyoxyalkylene ether polymer compound having perfluoroalkyl ether group in the side chain are particularly preferred because they have low foaming properties.As the perfluoroalkyl sulfonic acid compound, for example, perfluoroalkyl sulfonic acid, perfluoroalkyl sulfonate, etc. can be mentioned.As the perfluoroalkyl carboxylic acid compound, for example, perfluoroalkyl carboxylic acid, perfluoroalkyl carboxylate, etc. can be mentioned.As the polyoxyalkylene ether polymer compound having perfluoroalkyl ether group in the side chain, for example, sulfate ester salt of polyoxyalkylene ether polymer having perfluoroalkyl ether group in the side chain, salt of polyoxyalkylene ether polymer having perfluoroalkyl ether group in the side chain, etc. can be mentioned. Examples of counter ions of the salts in these fluorosurfactants include _Li , Na, K, _NH4 , _NH3CH2CH2OH , _NH2 ( _{CH2CH2OH ) 2} , and _NH ( _CH2CH2OH ) _{3 .}
Examples of amphoteric surfactants include lauryl aminopropionate, lauryl dimethyl betaine, stearyl dimethyl betaine, and lauryl dihydroxyethyl betaine.
Examples of nonionic surfactants include polyoxyethylene alkylphenyl ethers, polyoxyethylene alkyl esters, polyoxyethylene alkylamines, polyoxyethylene alkylamides, polyoxyethylene propylene block polymers, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, and ethylene oxide adducts of acetylene alcohol.
Examples of the anionic surfactant include polyoxyethylene alkyl ether acetates, dodecylbenzene sulfonates, laurates, and salts of polyoxyethylene alkyl ether sulfates.
These may be used alone or in combination of two or more.

The silicone surfactant is not particularly limited and can be appropriately selected depending on the purpose. Examples of the silicone surfactant include side-chain modified polydimethylsiloxane, both-end modified polydimethylsiloxane, one-end modified polydimethylsiloxane, and both-end side-chain modified polydimethylsiloxane. Polyether-modified silicone surfactants having a polyoxyethylene group or a polyoxyethylene polyoxypropylene group as the modifying group are particularly preferred because they exhibit good properties as aqueous surfactants.
Such surfactants may be synthesized appropriately or may be commercially available products, such as those available from BYK-Chemie Co., Ltd., Shin-Etsu Chemical Co., Ltd., Dow Corning Toray Silicone Co., Ltd., Nippon Emulsion Co., Ltd., and Kyoeisha Chemical Co., Ltd.
The polyether-modified silicone surfactant is not particularly limited and can be appropriately selected depending on the purpose. For example, it can be a surfactant represented by the general formula (S-1) in which a polyalkylene oxide structure is introduced into the Si part side chain of dimethylpolysiloxane.
(In the general formula (S-1), m, n, a, and b each independently represent an integer, R represents an alkylene group, and R′ represents an alkyl group.)
As the polyether-modified silicone surfactant, commercially available products can be used, for example, KF-618, KF-642, KF-643 (Shin-Etsu Chemical Co., Ltd.), EMALEX-SS-5602, SS-1906EX (Nihon Emulsion Co., Ltd.), FZ-2105, FZ-2118, FZ-2154, FZ-2161, FZ-2162, FZ-2163, FZ-2164 (Dow Corning Toray Silicone Co., Ltd.), BYK-33, BYK-387 (BYK-Chemie Co., Ltd.), TSF4440, TSF4452, TSF4453 (Toshiba Silicon Co., Ltd.), and the like.

As the fluorine-based surfactant, a compound having 2 to 16 fluorine-substituted carbon atoms is preferred, and a compound having 4 to 16 fluorine-substituted carbon atoms is more preferred.
Examples of the fluorine-based surfactant include perfluoroalkyl phosphate compounds, perfluoroalkyl ethylene oxide adducts, and polyoxyalkylene ether polymer compounds having a perfluoroalkyl ether group on the side chain, etc. Among these, polyoxyalkylene ether polymer compounds having a perfluoroalkyl ether group on the side chain are preferred because they have low foaming properties, and the fluorine-based surfactants represented by the general formulas (F-1) and (F-2) are particularly preferred.
In the compound represented by the above general formula (F-1), m is preferably an integer of 0 to 10, and n is preferably an integer of 0 to 40 in order to impart water solubility.
In the compound represented by the above general formula (F-2), Y is H, or CmF _2m+1 where m is an integer from 1 to 6, or CH ₂ CH(OH)CH ₂ -CmF _2m+1 where m is an integer from 4 to 6, or CpH _2p+1 where p is an integer from 1 to 19. n is an integer from 1 to 6. a is an integer from 4 to 14.
As the fluorine-based surfactant, commercially available products may be used. Examples of the commercially available products include Surflon S-111, S-112, S-113, S-121, S-131, S-132, S-141, and S-145 (all manufactured by Asahi Glass Co., Ltd.); Fullard FC-93, FC-95, FC-98, FC-129, FC-135, FC-170C, FC-430, and FC-431 (all manufactured by Sumitomo 3M Limited); Megafa F-470, F-1405, F-474 (all manufactured by Dainippon Ink & Chemicals, Inc.); Zonyl TBS, FSP, FSA, FSN-100, FSN, FSO-100, FSO, FS-300, UR, Capstone FS-30, FS-31, FS-3100, FS-34, FS-35 (all manufactured by Chemours); FT-110, FT- 250, FT-251, FT-400S, FT-150, FT-400SW (all manufactured by Neos Co., Ltd.), Polyfox PF-136A, PF-156A, PF-151N, PF-154, PF-159 (manufactured by Omnova), Unidyne DSN-403N (manufactured by Daikin Industries, Ltd.), and the like. Among these, preferred are those which have good print quality, particularly color development and paper adhesion. From the viewpoint of significantly improving the permeability, wettability and uniform dyeing property, FS-3100, FS-34 and FS-300 manufactured by Chemours Corporation, FT-110, FT-250, FT-251, FT-400S, FT-150 and FT-400SW manufactured by Neos Co., Ltd., Polyfox PF-151N manufactured by Omnova Co., Ltd. and Unidyne DSN-403N manufactured by Daikin Industries, Ltd. are particularly preferred.

The amount of surfactant contained is not particularly limited and can be selected appropriately depending on the purpose, but is preferably 0.001% by mass or more and 5% by mass or less, and more preferably 0.05% by mass or more and 5% by mass or less, relative to the mass of the liquid (pretreatment liquid) contained.

-Other ingredients-
If necessary, antifoaming agents, antiseptics, antifungals, rust inhibitors, pH adjusters, etc. may be added to the pretreatment liquid.

- Method for producing pretreatment liquid -
The pretreatment liquid can be obtained by dispersing or dissolving the components in an aqueous medium, and further stirring and mixing as necessary. Stirring and mixing can be performed using a stirrer using a normal stirring blade, a magnetic stirrer, a high-speed disperser, or the like.

- Properties of pretreatment liquid -
The physical properties of the pretreatment liquid are not particularly limited, and the viscosity, surface tension, pH, etc. can be appropriately selected depending on the purpose.
The viscosity of the pretreatment liquid is preferably 0.5 mPa·s or more and 30 mPa·s or less at 25° C. Here, the viscosity can be measured, for example, using a viscometer (device name: RE-550L, manufactured by Toki Sangyo Co., Ltd.).
The surface tension of the pretreatment liquid at 25° C. is preferably 45 mN/m or less, and more preferably 40 mN/m or less.
The pH of the pretreatment liquid is, for example, preferably 4 or more and 12 or less, and more preferably 6 or more and 10 or less.

<Ink>
The ink contains a compound represented by general formula (1), a coloring material, water, and an organic solvent, and, as necessary, a compound represented by general formula (2), a resin (excluding the compound represented by general formula (1)), a surfactant, and other components. Note that the water, organic solvent, surfactant, and other components can be the same as those in the pretreatment liquid described above, and therefore a description of these will be omitted.

-Compound represented by general formula (1) (polyvinyl alcohol)-
The ink contains a compound represented by the following general formula (1): The compound represented by general formula (1) is contained in the ink, and thereby suppresses a decrease in gloss and abrasion resistance of an image formed by the ink applied to an area to which a pretreatment liquid has been applied.
(In the above general formula (1), m and n each independently represent an integer.)

First, the reason why the inclusion of the compound represented by formula (1) can suppress the decrease in glossiness and the decrease in abrasion resistance will be described.
Generally, the pretreatment liquid is a liquid composition that causes the coloring material in the ink to aggregate and thicken when it comes into contact with the ink to be applied later, and therefore the coloring material in the ink is less uniformly dispersed when it comes into contact with the pretreatment liquid, which leads to a decrease in uniformity on the surface of the image formed by the ink, resulting in a problem of a decrease in gloss.
Furthermore, in an image formed by using a pretreatment liquid and an ink in combination to aggregate the coloring material in the ink and thicken the ink, the aggregated coloring material (hereinafter also referred to as an aggregate of coloring material) is present on the image surface, which causes a problem of abrasion resistance. This problem tends to become prominent when an image is formed on a recording medium that is a low-permeability substrate such as coated paper, thick paper, or paperboard, or when ink is applied to a recording medium to which a pretreatment liquid has been applied without heating.
In response to these problems, by incorporating in the ink a compound represented by general formula (1) having a degree of saponification of 63 to 100 and a degree of polymerization of 100 to 270, a large amount of resin can be present on the image surface, the unevenness of the image surface can be reduced, and a decrease in glossiness can be suppressed. Furthermore, the reduction in the unevenness of the image surface reduces the coefficient of friction, and the resin in the ink improves the adhesion of the color material to the recording medium, thereby suppressing a decrease in abrasion resistance.

Moreover, it is more preferable that the compound represented by general formula (1) has a degree of saponification of 63 or more and 100 or less, and a degree of polymerization of 100 or more and 270 or less. By having the degree of saponification and the degree of polymerization within this range, the decrease in gloss and the decrease in abrasion resistance can be further suppressed.

The compound represented by the general formula (1) may be appropriately synthesized or may be a commercially available product. Examples of commercially available products include JMR-3HH (manufactured by Nippon Vinyl Acetate & Poval Corporation), JMR-10HH (manufactured by Nippon Vinyl Acetate & Poval Corporation), JMR-3H (manufactured by Nippon Vinyl Acetate & Poval Corporation), JMR-10H (manufactured by Nippon Vinyl Acetate & Poval Corporation), JMR-3M (manufactured by Nippon Vinyl Acetate & Poval Corporation), JMR-8M (manufactured by Nippon Vinyl Acetate & Poval Corporation), and JMR-10M (manufactured by Nippon Vinyl Acetate & Poval Corporation). These may be used alone or in combination of two or more. Among these, JMR-10H (manufactured by Nippon Vinyl Acetate & Poval Corporation), JMR-8M (manufactured by Nippon Vinyl Acetate & Poval Corporation), and JMR-10M (manufactured by Nippon Vinyl Acetate & Poval Corporation) are preferred.

The content of the compound represented by general formula (1) is preferably 0.1% by mass or more and 10.0% by mass or less, and more preferably 1.0% by mass or more and 5.0% by mass or less, relative to the mass of the ink. By having the content be 0.1% by mass or more and 10.0% by mass or less, it is possible to further suppress the decrease in gloss and the decrease in abrasion resistance, and also to apply the ink uniformly to the recording medium.

- Coloring materials -
The coloring material is not particularly limited, and a pigment or a dye can be used. As the pigment, an inorganic pigment or an organic pigment can be used. These can be used alone or in combination of two or more kinds. Mixed crystals can also be used.

Examples of pigments that can be used include black pigments, yellow pigments, magenta pigments, cyan pigments, white pigments, green pigments, orange pigments, glossy pigments such as gold and silver pigments, and metallic pigments.

Inorganic pigments that can be used include titanium oxide, iron oxide, calcium carbonate, barium sulfate, aluminum hydroxide, barium yellow, cadmium red, and chrome yellow, as well as carbon black produced by known methods such as the contact method, furnace method, and thermal method.

As organic pigments, azo pigments, polycyclic pigments (e.g., phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, indigo pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments, etc.), dye chelates (e.g., basic dye chelates, acid dye chelates, etc.), nitro pigments, nitroso pigments, aniline black, etc. can be used. Of these pigments, those with good affinity with the solvent are preferably used. In addition, resin hollow particles and inorganic hollow particles can also be used.

Specific examples of pigments for black colors include carbon blacks (C.I. Pigment Black 7) such as furnace black, lamp black, acetylene black, and channel black, metals such as copper, iron (C.I. Pigment Black 11), and titanium oxide, and organic pigments such as aniline black (C.I. Pigment Black 1).

In addition, for color, C.I. Pigment Yellow 1, 3, 12, 13, 14, 17, 24, 34, 35, 37, 42 (yellow iron oxide), 53, 55, 74, 81, 83, 95, 97, 98, 100, 101, 104, 108, 109, 110, 117, 120, 138, 150, 153, 155, 180, 185, 213, C.I. Pigment Orange 5, 13, 16, 17, 36, 43, 51, C.I. Pigment Red 1, 2, 3, 5, 17, 22, 23, 31, 38, 48:2, 48:2 (Permanent Red 2B (Ca)), 48:3, 48:4, 49:1, 52:2, 53:1, 57:1 (Brilliant Carmine 6B), 60:1, 63:1, 63:2, 64:1, 81, 83, 88, 101 (Red ochre), 1 04, 105, 106, 108 (Cadmium Red), 112, 114, 122 (Quinacridone Magenta), 123, 146, 149, 166, 168, 170, 172, 177, 178, 179, 184, 185, 190, 193, 202, 207, 208, 209, 213, 219, 224, 254, 264, C.I. Pigment Violet 1 (Rhodamine Lake), 3, 5:1, 16, 19, 23, 38, C.I. Pigment Blue 1, 2, 15 (Phthalocyanine Blue), 15:1, 15:2, 15:3, 15:4 (Phthalocyanine Blue), 16, 17:1, 56, 60, 63, C.I. Pigment Green 1, 4, 7, 8, 10, 17, 18, 36, etc.

The dye is not particularly limited, and acid dyes, direct dyes, reactive dyes, and basic dyes can be used. One type of dye may be used alone, or two or more types may be used in combination.
As dyes, for example, 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, 225, 227, C.I. Direct Blue 1, 2, 15, 71, 86, 87, 98, 165, 199, 202, C.I. Directed Black 19, 38, 51, 71, 154, 168, 171, 195, C.I. Reactive Red 14, 32, 55, 79, 249, C.I. Reactive Black 3, 4, 35.

The content of the coloring material may be appropriately determined depending on the application of the ink, but is preferably 1.0% by mass to 15.0% by mass, more preferably 1.0% by mass to 10.0% by mass, based on the mass of the ink.

Methods for dispersing a pigment to obtain an ink include a method of introducing a hydrophilic functional group into the pigment to make it a self-dispersing pigment, a method of dispersing the pigment by coating the surface of the pigment with a resin, and a method of dispersing the pigment using a dispersant.
As a method for making a pigment self-dispersible by introducing a hydrophilic functional group into the pigment, for example, a method for making the pigment dispersible in water by adding a functional group such as a sulfone group or a carboxyl group to the pigment (e.g., carbon) can be mentioned.
As a method for dispersing a pigment by coating its surface with a resin, a method for encapsulating the pigment in a microcapsule to make it dispersible in water can be mentioned. This can be called a resin-coated pigment. In this case, it is not necessary for all the pigments used to be coated with resin, and uncoated pigments and partially coated pigments may be included.
Examples of the method of dispersing using a dispersant include a method of dispersing using a known low molecular weight dispersant or a polymeric dispersant, such as a surfactant. As the dispersant, for example, an anionic surfactant, a cationic surfactant, an amphoteric surfactant, a nonionic surfactant, etc. can be used depending on the pigment. RT-100 (nonionic surfactant) manufactured by Takemoto Oil Co., Ltd. and a sodium naphthalenesulfonate formalin condensate can also be suitably used as a dispersant. One type of dispersant may be used alone, or two or more types may be used in combination.

-Compound represented by formula (2) (polyoxyethylene alkyl ether)-
The ink may contain a compound represented by the following general formula (2). By containing the compound represented by general formula (2) in the ink, the ink becomes more likely to wet and spread when applied to a recording medium. As a result, the ink spreads thinly and uniformly on the surface of the recording medium, shortening the time it takes for the ink applied to the recording medium to dry. In addition, the permeability of the ink into the recording medium is also improved. As a result, the drying property of the ink is improved, the formed image is stronger, and the abrasion resistance is further improved. In addition, the glossiness is further improved due to the effect of making the ink more likely to wet and spread when applied to a recording medium and the effect of promoting the melting of the resin in the ink by improving the drying property of the ink.
(In the above general formula (2), n represents an integer of 3 or more and 11 or less.)

As mentioned above, n in general formula (2) represents an integer of 3 or more and 11 or less. When n is an integer of 3 or more and 11 or less, the ink wets and spreads more easily when applied to a recording medium. This allows the ink to spread evenly and thinly over the surface of the recording medium, shortening the time it takes for the ink applied to the recording medium to dry. In addition, the ink's permeability into the recording medium is improved. This improves the drying properties of the ink, making the formed image stronger and further improving abrasion resistance.

As the compound represented by the general formula (2), a compound appropriately synthesized or a commercially available product may be used. Examples of commercially available products include TRITON HW-1000 (manufactured by Dow Chemical Co.), TERGITOL TMN-3 (manufactured by Dow Chemical Co.), TERGITOL TMN-6 (manufactured by Dow Chemical Co.), TERGITOL TMN-100X (manufactured by Dow Chemical Co.), and TERGITOL TMN-10 (manufactured by Dow Chemical Co.). These may be used alone or in combination of two or more types. Among these, TRITON HW-1000 (manufactured by Dow Chemical Co.) and TERGITOL TMN-6 (manufactured by Dow Chemical Co.) are preferred.

The content of the compound represented by formula (2) is preferably 0.001% by mass or more and 1.5% by mass or less, and more preferably 0.001% by mass or more and 0.2% by mass or less, relative to the mass of the ink. When the content is 0.001% by mass or more and 1.5% by mass or less, it is possible to improve abrasion resistance while suppressing the occurrence of beading.

-resin-
The ink may contain a resin (excluding the compound represented by formula (1)). The type of resin is not particularly limited and may be appropriately selected depending on the purpose, and examples thereof include urethane resin, polyester resin, acrylic resin, vinyl acetate resin, styrene resin, butadiene resin, styrene-butadiene resin, vinyl chloride resin, acrylic-styrene resin, and acrylic-silicone resin.
Resin particles made of these resins may be used. The resin particles may be dispersed in water as a dispersion medium in the form of a resin emulsion, and mixed with materials such as coloring materials and organic solvents to obtain an ink. The resin particles may be appropriately synthesized or may be commercially available. These may be used alone or in combination of two or more types of resin particles.

The volume average particle size of the resin particles is not particularly limited and can be appropriately selected depending on the purpose. From the viewpoint of obtaining good fixing property and high image hardness, the volume average particle size is preferably 10 nm or more and 1,000 nm or less, more preferably 10 nm or more and 200 nm or less, and particularly preferably 10 nm or more and 100 nm or less.
The volume average particle size can be measured, for example, using a particle size analyzer (Nanotrac Wave-UT151, manufactured by Microtrac Bell Co., Ltd.).

There are no particular limitations on the resin content, and it can be selected appropriately depending on the purpose, but from the standpoint of fixation and ink storage stability, it is preferably 1% by mass or more and 30% by mass or less, and more preferably 5% by mass or more and 20% by mass or less, of the total amount of ink.

-Ink manufacturing method-
The ink can be obtained by dispersing or dissolving the components in an aqueous medium, and further stirring and mixing as necessary. Stirring and mixing can be performed using a stirrer using a normal stirring blade, a magnetic stirrer, a high-speed disperser, or the like.

- Ink properties -
The physical properties of the ink are not particularly limited and can be appropriately selected depending on the purpose. For example, it is preferable that the viscosity, surface tension, pH, etc. are within the following ranges.
The viscosity of the ink at 25° C. is preferably 5 mPa·s or more and 30 mPa·s or less, and more preferably 5 mPa·s or more and 25 mPa·s or less, in terms of improving the print density and character quality and obtaining good ejection properties. Here, the viscosity can be measured using, for example, a rotational viscometer (RE-80L, manufactured by Toki Sangyo Co., Ltd.). The measurement conditions are 25° C., a standard cone rotor (1°34′×R24), a sample liquid volume of 1.2 mL, a rotation speed of 50 rpm, and 3 minutes.
The static surface tension of the ink is preferably 25 mN/m or less, more preferably 22 mN/m or less, at 25° C., from the viewpoint of suitably leveling the ink on the recording medium and shortening the drying time of the ink. When an ink with such a low static surface tension is used, the ink applied to the recording medium after the pretreatment liquid is applied spreads more, and the ink is accelerated in evaporation and drying and penetration and drying. Therefore, by using a pretreatment liquid and an ink with a low static surface tension, the amount of remaining solvent in the image formed by the ink is reduced, making it possible to form a stronger image and further improving the abrasion resistance.
The pH of the ink is preferably 7 or more and 12 or less, and more preferably 8 or more and 11 or less, from the viewpoint of preventing corrosion of metal members that come into contact with the ink.

<<Recording Media>>
The recording medium is not particularly limited and may be plain paper, glossy paper, special paper, cloth, or the like, but is particularly suitable for use with low permeability substrates (low absorbency substrates).
The low-permeability substrate means a substrate having a surface with low water permeability, absorbency, or adsorption, and includes materials that have many cavities inside but are not open to the outside. Examples of low-permeability substrates include coated paper used in commercial printing and recording media such as paperboard coated with recycled paper pulp in the middle and back layers.
The recording medium may be cut paper on which one print unit can be printed, or continuous paper or roll paper on which multiple print units can be printed in the transport direction of the recording medium.

<Low permeability substrate>
An example of a low-permeability substrate is a recording medium such as coated paper having a support and a surface layer provided on at least one side of the support, and further having other layers as necessary.

In a recording medium having a support and a surface layer, the amount of pure water transferred to the recording medium in a contact time of 100 ms, as measured with a dynamic scanning absorptiometer, is preferably 2 mL/ ^m2 or more and 35 mL/m2 or ^less , and more preferably 2 mL/m2 or ^more and 10 mL/ ^m2 or less.

If the amount of ink and pure water transferred during a contact time of 100 ms is too small, beading may occur more easily, and if it is too large, the ink dot diameter after image formation may be smaller than the desired diameter.

The amount of pure water transferred to the recording medium in a contact time of 400 ms as measured by a dynamic scanning absorptiometer is preferably 3 mL/m ² or more and 40 mL/m ² or less, and more preferably 3 mL/m ² or more and 10 mL/m ² or less.

If the amount of transfer at a contact time of 400 ms is small, the drying will be insufficient, and if the amount is too large, the gloss of the image area after drying may be prone to decrease. The amount of pure water transferred to the recording medium at contact times of 100 ms and 400 ms can both be measured on the side of the recording medium that has the surface layer.

The dynamic scanning absorbtometer (DSA, Journal of the Paper and Pulp Technology Association, Vol. 48, May 1994, pp. 88-92, Shigenori Kuga) is a device that can accurately measure the amount of absorbed liquid in an extremely short time. The dynamic scanning absorbtometer automates the measurement by directly reading the absorption speed from the movement of the meniscus in the capillary, scanning the absorption head in a spiral on a disk-shaped sample, automatically changing the scanning speed according to a preset pattern, and measuring the required number of points on one sample.

The liquid supply head for the paper sample is connected to the capillary via a Teflon (registered trademark) tube, and the position of the meniscus in the capillary is automatically read by an optical sensor. Specifically, the amount of transferred pure water or ink can be measured using a dynamic scanning absorptiometer (K350 series D type, manufactured by Kyowa Seiko Co., Ltd.).

The transfer amounts at contact times of 100 ms and 400 ms can be calculated by interpolation from the measured values of the transfer amounts at contact times adjacent to each contact time.

- Support -
The support is not particularly limited and can be appropriately selected depending on the purpose. Examples of the support include paper mainly made of wood fibers, and sheet-like materials such as nonwoven fabric mainly made of wood fibers and synthetic fibers.
The thickness of the support is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 50 μm to 300 μm. The basis weight of the support is preferably 45 g/m ² to 290 g/m ² .

- Surface layer -
The surface layer contains a pigment and a binder, and may further contain a surfactant and other components as required.
As the pigment, an inorganic pigment or a combination of an inorganic pigment and an organic pigment can be used. Examples of inorganic pigments include kaolin, talc, heavy calcium carbonate, light calcium carbonate, calcium sulfite, amorphous silica, titanium white, magnesium carbonate, titanium dioxide, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, zinc hydroxide, and chlorite. The amount of inorganic pigment added is preferably 50 parts by mass or more per 100 parts by mass of the binder.
Examples of organic pigments include water-soluble dispersions of styrene-acrylic copolymer particles, styrene-butadiene copolymer particles, polystyrene particles, polyethylene particles, etc. The amount of organic pigment added is preferably 2 parts by mass to 20 parts by mass with respect to 100 parts by mass of the total pigments in the surface layer.
As the binder, it is preferable to use an aqueous resin. As the aqueous resin, at least one of a water-soluble resin and a water-dispersible resin can be suitably used. The water-soluble resin is not particularly limited and can be appropriately selected according to the purpose, and examples thereof include polyvinyl alcohol, cation-modified polyvinyl alcohol, acetal-modified polyvinyl alcohol, polyester, polyurethane, and polyester and polyurethane.
The surfactant contained in the surface layer as necessary is not particularly limited and can be appropriately selected depending on the purpose, but any of anionic surfactants, cationic surfactants, amphoteric surfactants, and nonionic surfactants can be used.
The method for forming the surface layer is not particularly limited and can be appropriately selected depending on the purpose, and can be performed by impregnating or coating the support with the liquid that constitutes the surface layer. The amount of the liquid that constitutes the surface layer is not particularly limited and can be appropriately selected depending on the purpose, and is preferably 0.5 g/ ^m2 to 20 g/ ^m2 , and more preferably 1 g/ ^m2 to 15 g/ ^m2 in terms of solid content.

<<Recordings>>
In the present disclosure, the term "recorded matter" refers to a structure having a recording medium and an image formed by applying the above-mentioned pretreatment liquid and ink to the recording medium. The recorded matter may be a recording medium to which the pretreatment liquid and ink have been applied that has been dried, or may be a recording medium that has not been dried but is in a wet state, or may be a recording medium to which another liquid composition has been applied in addition to the pretreatment liquid and ink.
The image has at least a polyvalent metal salt and a compound represented by general formula (1) derived from a pretreatment liquid, and a colorant and a compound represented by general formula (1) derived from an ink, and, depending on the compositions of the pretreatment liquid and the ink, also has a compound represented by general formula (2) and the like.

<<Image forming apparatus, image forming method>>
The image forming apparatus has a pretreatment liquid storage means for storing a pretreatment liquid, an ink storage means for storing ink, a pretreatment liquid applying means for applying the pretreatment liquid to the recording medium, and an ink applying step for applying ink to the area of the recording medium to which the pretreatment liquid has been applied, and may have other configurations as necessary, such as a heating means for heating the pretreatment liquid or various liquids such as ink applied to the recording medium.
The image forming method includes a pretreatment liquid applying step of applying a pretreatment liquid to a recording medium, and an ink applying step of applying ink to the area of the recording medium to which the pretreatment liquid has been applied, and may include other steps as necessary, such as a heating step of heating the pretreatment liquid or various liquids such as ink applied to the recording medium.

An example of an image forming apparatus and an image forming method using the image forming apparatus will be described with reference to Fig. 1. Fig. 1 is a schematic diagram showing an example of an image forming apparatus.
The image forming apparatus 1 shown in FIG. 1 includes a paper feeding means 3 that feeds a recording medium 2, a pretreatment liquid applying means 4 that applies pretreatment liquid supplied from a pretreatment liquid storage means that stores a pretreatment liquid to the recording medium 2, an ink applying means 5 that applies ink supplied from an ink storage means that stores ink to an area of the recording medium 2 to which the pretreatment liquid has been applied, a first heating means 6-1 and a second heating means 6-2 that heat and dry the recording medium 2 to which the pretreatment liquid and ink have been applied, and a winding means 7 that winds up the recording medium after drying.

The paper feed means 3 is a means for feeding the recording medium 2 to a position where the pretreatment liquid application means 4 applies pretreatment liquid and where the ink application means 5 applies ink. In FIG. 1, continuous paper is used as the recording medium 2. Continuous paper is a recording medium that is continuous in the transport direction during image formation and is longer than the length of a print unit (one page) in the transport direction. As the continuous paper, for example, rolled rolled paper can be used. In FIG. 1, the paper feed means 3 is a paper feed roller, and the recording medium 2 rolled up in a roll is set in the paper feed means 3.

The pretreatment liquid application means 4 is a means for applying a pretreatment liquid to the fed recording medium 2, and executes the above-mentioned pretreatment liquid application process. The pretreatment liquid application means 4 shown in FIG. 1 is a roller application method in which a roller applies a pretreatment liquid to the recording medium 2, but it may also be a means for applying the pretreatment liquid by an inkjet recording method. In the case of a means for applying the pretreatment liquid by an inkjet recording method, it is preferable that the means has one or more ejection heads corresponding to the treatment liquid.

The ink application means 5 is a means for applying ink to the fed recording medium 2 to form an image, and executes the ink application process described above. The ink application means 5 is preferably a means for applying ink by an inkjet recording method. In the case of a means for applying ink by an inkjet recording method, it is preferable that the ink application means has, for example, four ejection heads corresponding to black (K), cyan (C), magenta (M), and yellow (Y).

The inkjet recording method is a method in which a stimulus is applied to a liquid composition to eject the liquid composition. There are no particular limitations on the stimulus, and it can be appropriately selected depending on the purpose. Examples of the stimulus include heat (temperature), pressure, vibration, and light. One type of stimulus may be used alone, or two or more types may be used in combination. Of these, heat and pressure are preferably used.

Examples of the liquid composition ejection mode used in the liquid composition include a piezoelectric method in which a piezoelectric element is used as a pressure generating means for pressurizing the liquid composition in the liquid composition flow path to deform a vibration plate that forms the wall of the liquid composition flow path, thereby changing the internal volume of the liquid composition flow path and ejecting liquid composition droplets; a thermal method in which a heating resistor is used to heat the liquid composition in the liquid composition flow path and generate bubbles; and an electrostatic method in which a vibration plate that forms the wall of the liquid composition flow path and an electrode are arranged opposite each other, and the vibration plate is deformed by electrostatic force generated between the vibration plate and the electrode to change the internal volume of the liquid composition flow path and eject liquid composition droplets.

The size of the droplets of the liquid composition to be ejected is preferably, for example, 3.0 pL or more and 4.5 pL or less, the ejection speed is preferably 5 m/s or more and 20 m/s or less, the drive frequency is preferably 1 kHz or more, and the resolution is preferably 300 dpi or more.

The ejection head used in the inkjet recording method may be provided with a container such as a sub-tank that contains the liquid composition. The liquid composition contained in the ejection head may be supplied from another container as a main tank. Examples of the other container include a cartridge or bottle that contains the liquid composition and is casing made of resin or the like. In the cartridge, the liquid composition may be contained in an aluminum pouch with an inner bag made of resin such as polyethylene.

The first heating means 6-1 is not particularly limited as long as it heats the recording medium 2 from the side on which the pretreatment liquid and ink have been applied, and examples of such means include a hot air device that applies hot air or an infrared ray irradiation device that irradiates infrared rays. The second heating means 6-2 is not particularly limited as long as it heats the recording medium 2 from the side opposite the side on which the pretreatment liquid and ink have been applied, and examples of such means include a heating roller. The heating roller may have a heater provided in the roller portion, or may have a heater provided outside the roller portion to heat the roller portion.

The winding means 7 is a means for winding up the recording medium 2 that has been fed by the paper feeding means 3, has had pretreatment liquid applied by the pretreatment liquid applying means 4, has had ink applied by the ink applying means 5, and has been heated by the first heating means 6-1 and the second heating means 6-2. By the winding means 7 winding up the recording medium 2, the recording medium 2 is transported in the transport direction indicated by the arrow in FIG. 1.

In addition, although Fig. 1 shows a case where roll paper is used as the recording medium, the recording medium is not limited to this. As other recording media, for example, continuous paper that is not wound in a roll, such as continuous paper folded at predetermined intervals or continuous forms with cuttable perforations formed at predetermined intervals, may be used. In this way, when a recording medium other than roll paper is used, there is no need to wind up the recording medium, so the winding means 7 shown in Fig. 1 can be omitted.
In addition, in the image forming apparatus according to the present embodiment, cut sheets may be used as the recording medium instead of continuous paper. A cut sheet is a recording medium that is independent for each print unit (one page) in the transport direction during image formation.
Furthermore, each of the means such as the pretreatment liquid application means 4, the ink application means 5, and the winding means 7 is not limited to being provided in the image forming apparatus 1 which is a single device, but for example, each of the means such as the pretreatment liquid application means 4, the ink application means 5, and the winding means 7 may be distributed and present in separate devices.
The image forming apparatus is not limited as long as it forms an image by applying a pretreatment liquid and ink to a recording medium. Examples of the image forming apparatus include a printer, a facsimile machine, a copying machine, a printer/facsimile/copying machine combination, a three-dimensional modeling apparatus, and the like.

The following describes examples of the present invention, but the present invention is not limited to these examples.

<Synthesis of copolymer>
--Synthesis Example of Copolymer A--
A stirring device, a dropping device, a temperature sensor, and a reaction vessel equipped with a reflux device having a nitrogen introduction device at the top of the reaction vessel of an automatic polymerization reaction apparatus (Todoroki Sangyo Co., Ltd., polymerization tester DSL-2AS type) were charged with 550 g of methyl ethyl ketone, and the inside of the reaction vessel was replaced with nitrogen while stirring. After heating to 80 ° C. while maintaining the inside of the reaction vessel in a nitrogen atmosphere, a mixed solution of 75.0 g of 2-hydroxyethyl methacrylate, 77.0 g of methacrylic acid, 80.0 g of styrene, 150.0 g of butyl methacrylate, 98.0 g of butyl acrylate, 20.0 g of methyl methacrylate, and 40.0 g of "Perbutyl (registered trademark) O" (manufactured by NOF Corporation) was dropped over 4 hours by the dropping device. After the dropwise addition was completed, the reaction was continued for a further 15 hours at the same temperature to obtain a methyl ethyl ketone solution of an anionic group-containing styrene-acrylic copolymer A having an acid value of 100 mgKOH/g, a weight average molecular weight of 21,000, and a glass transition temperature Tg (calculated value) of 31° C. After the reaction was completed, a portion of the methyl ethyl ketone was distilled off under reduced pressure to obtain a styrene-acrylic copolymer A solution in which the nonvolatile content was adjusted to 50% by mass.

<Preparation of Pigment Dispersion>
--Preparation Example of Pigment Dispersion 1--
Into a mixing tank equipped with a cooling jacket, 1,000 g of copper phthalocyanine (SEIKALIGHT BLUE A612, manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.), 800 g of the anionic group-containing styrene-acrylic copolymer A solution, 143 g of a 10% by mass aqueous sodium hydroxide solution, 100 g of methyl ethyl ketone, and 1,957 g of water were charged and mixed with stirring.
The resulting mixture was passed through a dispersing device (manufactured by Nippon Coke & Engineering Co., Ltd., SC Mill SC100) filled with zirconia beads having a diameter of 0.3 mm, and dispersed for 6 hours by a circulation method (a method in which the dispersion liquid coming out of the dispersing device is returned to the mixing tank). The rotation speed of the dispersing device was 2,700 rpm, and cold water was passed through the cooling jacket so that the temperature of the dispersion liquid was kept below 40 ° C. After dispersion was completed, the stock dispersion was extracted from the mixing tank, and then the mixing tank and the dispersing device flow path were washed with 10,000 g of water, and the stock dispersion liquid was combined to obtain a diluted dispersion liquid. The diluted dispersion liquid was placed in a glass distillation apparatus, and the entire amount of methyl ethyl ketone and a part of the water were distilled off. After cooling to room temperature, 10% by mass hydrochloric acid was dropped while stirring to adjust the pH to 4.5, and the solid content was filtered with a Nutsche type filtration device (manufactured by Nippon Chemical Machinery Co., Ltd., a pressure filter) and washed with water. The cake was placed in a container, and 200 g of a 20 mass % aqueous potassium hydroxide solution was added, followed by dispersion using a Disper (TK Homo Disper, manufactured by Primix Corporation). Water was further added to adjust the non-volatile content, thereby obtaining Pigment Dispersion 1 in which carbon black with a non-volatile content of 20 mass % was dispersed in an aqueous medium as composite particles coated with a carboxyl group-containing styrene-acrylic copolymer neutralized in potassium hydroxide.

--Preparation Example of Pigment Dispersion 2--
Pigment Dispersion 2 was obtained in the same manner as in Preparation Example 1 of Pigment Dispersion 1, except that the copper phthalocyanine in Preparation Example 1 of Pigment Dispersion 1 was changed to carbon black (product name: Raven 1080, manufactured by Columbian Carbon Japan Co., Ltd.).

<Adjustment of Varnish>
- Example of Varnish 1 preparation -
Varnish 1 was obtained by mixing 25% by mass of polyvinyl alcohol represented by the above general formula (1) (product name: JMR10H, polymerization degree: 270, saponification degree: 81, manufactured by Nippon Vinyl Acetate & Poval Co., Ltd.) and 75% by mass of ion-exchanged water at room temperature for 2 hours with stirring.

-Adjustment examples of varnishes 2 to 4, 7, and 8-
Varnishes 2 to 4, 7, and 8 were obtained in the same manner as in Preparation Example 1 of Varnish 1, except that the polyvinyl alcohol in Preparation Example 1 of Varnish 1 was changed to the polyvinyl alcohol represented by the above general formula (1) shown in Tables 1 to 3 below.

- Example of Varnish 5 preparation -
25% by mass of polyvinyl alcohol represented by the above general formula (1) (product name: JMR3HH, degree of polymerization: 100, degree of saponification: 98.5, manufactured by Nippon Vinyl Acetate & Poval Co., Ltd.) and 75% by mass of ion-exchanged water were mixed with stirring at room temperature for 1 hour, then heated to 90° C. and stirred for another 1 hour. The mixture was then allowed to cool to room temperature, thereby obtaining varnish 5.

-Adjustment examples of varnish 6 and 9-
Varnishes 6 and 9 were obtained in the same manner as in Preparation Example 5 of Varnish 5, except that the polyvinyl alcohol in Preparation Example 5 of Varnish 5 was changed to the polyvinyl alcohol represented by the above general formula (1) shown in Tables 1 to 3 below.

-Other reference adjustment examples-
In the preparation example of varnish 1, when the polyvinyl alcohol represented by the above general formula (1) (product name: JMR10H, degree of polymerization: 270, degree of saponification: 81, manufactured by Nippon Vinyl Acetate & Poval Co., Ltd.) was changed to another polyvinyl alcohol represented by the above general formula (1) (product name: JMR10L, degree of polymerization: 250, degree of saponification: 37, manufactured by Nippon Vinyl Acetate & Poval Co., Ltd.), the polyvinyl alcohol did not dissolve in ion-exchanged water, and a varnish could not be obtained.

<Ink adjustment>
--Adjustment example of Ink 1--
22.0% by mass of glycerin, 11.0% by mass of 1,3-butanediol, 2.0% by mass of 1,3-octanediol, 0.1% by mass of polyoxyethylene alkyl ether represented by the above general formula (2) (product name: TRITON HW-1000, n=6, manufactured by Dow Chemical Company), and ion-exchanged water were stirred for 1 hour to uniformly mix, and then 10.0% by mass of Varnish 1 was added and stirred for 1 hour to uniformly mix, after which Pigment Dispersion 1 was added so that the solid content was 8.0% by mass, and stirred for 1 hour to uniformly mix. This mixture was pressure-filtered using a polyvinylidene fluoride membrane filter having an average pore size of 0.8 μm to remove coarse particles and dust, thereby obtaining Ink 1.

--Adjustment examples for inks 2 to 16--
Inks 2 to 16 were obtained in the same manner as in Preparation Example of Ink 1, except that the ink composition was changed to the composition shown in Tables 1 to 3 below.
In Tables 1 to 3, the units of each number for the composition are "mass %." The content of the varnish represents the total amount, and the content of the coloring material (pigment dispersions 1 and 2) represents the solid content.

<Preparation of pretreatment solution>
--Preparation example of pretreatment liquid 1--
12.0% by mass of varnish 1, 0.1% by mass of polyoxyethylene alkyl ether represented by the above general formula (2) (product name: TRITON HW-1000, manufactured by Dow Chemical Company), 25.6% by mass of magnesium nitrate hexahydrate (manufactured by Showa Chemical Co., Ltd.), and 29.6% by mass of glycerin were added and stirred for 1 hour to uniformly mix. Further, 32.7% by mass of ion-exchanged water was added to make the total 100% by mass, and the mixture was stirred for 1 hour to uniformly mix, thereby obtaining pretreatment liquid 1.

--Preparation examples of pretreatment solutions 2 to 17--
Pretreatment liquids 2 to 17 were obtained in the same manner as in Preparation Example 1 of pretreatment liquid 1, except that the composition of the pretreatment liquid was changed to the composition shown in Tables 4 to 6 below.
In Tables 4 to 6, the units of each number for the composition are "mass %." The content of the varnish indicates the total amount.

Details of each component in Tables 1 to 6 are as follows:

-Compound represented by formula (1)-
JMR10H (product name: JMR10H, degree of saponification: 81, degree of polymerization: 270, manufactured by Nippon Vinyl Acetate & Poval Co., Ltd.)
JMR3H (product name: JMR3H, degree of saponification: 81, degree of polymerization: 100, manufactured by Nippon Vinyl Acetate & Poval Co., Ltd.)
JMR10M (product name: JMR10M, degree of saponification: 63, degree of polymerization: 270, manufactured by Nippon Vinyl Acetate & Poval Co., Ltd.)
JMR3M (product name: JMR3M, degree of saponification: 63, degree of polymerization: 100, manufactured by Nippon Vinyl Acetate & Poval Co., Ltd.)
JMR3HH (product name: JMR3HH, degree of saponification: 98.5, degree of polymerization: 100, manufactured by Nippon Vinyl Acetate & Poval Co., Ltd.)
JMR10HH (product name: JMR10HH, degree of saponification: 98.5, degree of polymerization: 250, manufactured by Nippon Vinyl Acetate & Poval Co., Ltd.)
JMR20M (product name: JMR20M, degree of saponification: 65, degree of polymerization: 370, manufactured by Nippon Vinyl Acetate & Poval Co., Ltd.)
JMR20H (product name: JMR20H, degree of saponification: 80, degree of polymerization: 375, manufactured by Nippon Vinyl Acetate & Poval Co., Ltd.)
PVA103 (product name: PVA103, degree of saponification: 98.5, degree of polymerization: 300, manufactured by Kuraray Co., Ltd.)

-Compound represented by formula (2)-
HW-1000 (product name: TRITON HW-1000, n=6, manufactured by The Dow Chemical Company)
TMN-3 (product name: TERGITOL TMN-3, n=3, manufactured by The Dow Chemical Company)
TMN-6 (product name: TERGITOL TMN-6, n=8, manufactured by The Dow Chemical Company)
TMN-100X (product name: TERGITOL TMN-100X, n=9, manufactured by The Dow Chemical Company)
TMN-10 (product name: TERGITOL TMN-10, n=11, manufactured by The Dow Chemical Company)

-resin-
Rosin modified maleic acid resin (product name: Harimac R-100, manufactured by Harima Chemicals Co., Ltd.)

-Surfactants-
E1010 (product name: E1010, manufactured by Nissin Chemical Industry Co., Ltd.)
- DSN-403N (product name: Unidyne DSN-403N, polyoxyethylene perfluoroalkyl ether, manufactured by Daikin Industries, Ltd.)
・Unisafe A-LY (product name: Unisafe A-LY, nonionic surfactant, manufactured by NOF Corporation)

- Polyvalent metal salts -
Magnesium nitrate hexahydrate, manufactured by Showa Chemical Co., Ltd. Calcium nitrate tetrahydrate, manufactured by Showa Chemical Co., Ltd.

<Preparation of Ink Set>
(Examples 1 to 24, Comparative Examples 1 to 7)
The pretreatment liquids 1 to 17 and inks 1 to 16 prepared as described above were combined as shown in Table 7 below to prepare ink sets of Examples 1 to 24 and Comparative Examples 1 to 7.
Next, the gloss and abrasion resistance of each ink set were evaluated as follows, and the results are shown in Table 7 below.

[Glossiness]
Using the image forming apparatus shown in FIG. 1, the pretreatment liquid was applied to a recording medium (Oji Paper: OK top coat + [basis weight: 127.8 gsm]) so that the application amount was 0.9 g/m ² , and then ink was ejected onto the area of the recording medium to which the pretreatment liquid was applied, to obtain a print sample 1. Next, the pretreatment liquid was not applied to the recording medium (Oji Paper: OK top coat + [basis weight: 127.8 gsm]), and ink was ejected onto the recording medium to obtain a print sample 2. Note that a solid image of 3 cm square formed with a dot pattern was used as the print chart. Next, the 60° gloss of each of the print sample 1 to which the treatment liquid was applied and the print sample 2 to which the treatment liquid was not applied was measured using a gloss meter (product name: Micro-Tri-Gloss μ, manufactured by Toyo Seiki Seisakusho), and the "glossiness" was evaluated based on the following evaluation criteria. Note that a rating of B or higher was evaluated as being practical.
As the ink application means of the image forming apparatus, a discharge head mounted on the image forming apparatus (IPSiO GXe-5500, manufactured by Ricoh Co., Ltd.) was used.
(Evaluation Criteria)
A: The gloss difference between print sample 1 and print sample 2 is less than 2. B: The gloss difference between print sample 1 and print sample 2 is 2 or more and less than 10. C: The gloss difference between print sample 1 and print sample 2 is 10 or more.

[Abrasion resistance]
Using the image forming apparatus shown in FIG. 1, the pretreatment liquid was applied to a recording medium (NEW-DV, manufactured by Hokuetsu Corporation, basis weight: 450 gsm) so that the application amount was 0.9 g/ ^m2 , and then ink was ejected onto the area of the recording medium where the pretreatment liquid was applied, followed by heating and drying to obtain a print sample. Note that a 3 cm square solid image formed with a dot pattern was used as the print chart. Next, the 3 cm square solid image was rubbed with a fingernail 30 seconds after the heat drying was completed, and the image quality was visually observed, and the "abrasion resistance (nail scratch)" was evaluated based on the following evaluation criteria. A rating of B or higher was evaluated as being practical.
As the ink application means of the image forming apparatus, a discharge head mounted on an image forming apparatus (IPSiO GXe-5500, manufactured by Ricoh Co., Ltd.) was used.
(Evaluation Criteria)
A: No scratches are caused by fingernail scratches, and almost no change in image density is observed. B: No scratches are caused by fingernail scratches, but image density changes. C: Small scratches are caused by fingernail scratches. D: Clear scratches are caused by fingernail scratches.

REFERENCE SIGNS LIST 1 Image forming apparatus 2 Recording medium 3 Paper supply means 4 Pretreatment liquid applying means 5 Ink applying means 6-1 First heating means 6-1 Second heating means 7 Winding means

Patent No. 5346751

Claims (8)

An ink set including a pretreatment liquid to be applied to a recording medium, and an ink to be applied to an area of the recording medium to which the pretreatment liquid has been applied,
The pretreatment liquid contains a polyvalent metal salt, water, an organic solvent, and a compound represented by the following general formula (1):
The ink contains a colorant, water, an organic solvent, and a compound represented by the following general formula (1):
the compound represented by formula (1) contained in the pretreatment liquid has a degree of saponification of 63 or more and 100 or less and a degree of polymerization of 100 or more and 270 or less.
(In the above general formula (1), m and n each independently represent an integer.) The ink set according to claim 1, wherein the compound represented by the general formula (1) contained in the pretreatment liquid has a degree of saponification of 63 or more and 81 or less, and a degree of polymerization of 100 or more and 270 or less. The ink set according to claim 1 or 2, wherein the compound represented by the general formula (1) contained in the ink has a degree of saponification of 63 or more and 100 or less, and a degree of polymerization of 100 or more and 270 or less. The ink set according to claim 1 , wherein the pretreatment liquid further contains a compound represented by the following general formula (2):
(In the above general formula (2), n represents an integer of 3 or more and 11 or less.) The ink set according to claim 4, wherein in the compound represented by the general formula (2) contained in the pretreatment liquid, n represents an integer of 6 or more and 8 or less. The ink set according to claim 1 , further comprising a compound represented by the following general formula (2):
(In the above general formula (2), n represents an integer of 3 or more and 11 or less.) 1. An image forming method comprising: a pretreatment liquid applying step of applying a pretreatment liquid to a recording medium; and an ink applying step of applying ink to an area of the recording medium to which the pretreatment liquid has been applied,
The pretreatment liquid contains a polyvalent metal salt, water, an organic solvent, and a compound represented by the following general formula (1):
The ink contains a colorant, water, an organic solvent, and a compound represented by the following general formula (1):
The image forming method according to the present invention, wherein the compound represented by the general formula (1) contained in the pretreatment liquid has a degree of saponification of 63 or more and 100 or less and a degree of polymerization of 100 or more and 270 or less.
(In the above general formula (1), m and n each independently represent an integer.) An image forming apparatus comprising: a pretreatment liquid container that contains a pretreatment liquid; an ink container that contains ink; a pretreatment liquid applying device that applies the pretreatment liquid to a recording medium; and an ink applying step that applies the ink to an area of the recording medium to which the pretreatment liquid has been applied,
The pretreatment liquid contains a polyvalent metal salt, water, an organic solvent, and a compound represented by the following general formula (1):
The ink contains a colorant, water, an organic solvent, and a compound represented by the following general formula (1):
the compound represented by the general formula (1) contained in the pretreatment liquid has a degree of saponification of 63 or more and 100 or less and a degree of polymerization of 100 or more and 270 or less;
(In the above general formula (1), m and n each independently represent an integer.)