JP7661801B2 - Printing method and printing device - Google Patents

Description

The present invention relates to a printing method and a printing device.

In recent years, inkjet printers are not only used for home use; the technology to print images on packaging materials for food, beverages, daily necessities, etc. has been developed. Examples of substrates for packaging applications include cardboard.

Methods for printing on cardboard can be broadly divided into two types: the pre-print method, in which an image is printed on the base cardboard paper (surface liner paper) with printing ink, and then the core and back liner paper are attached using a corrugator to produce cardboard, and the post-print method, in which an image is printed on the surface liner paper of the already attached cardboard with printing ink.

Conventionally, offset printing, flexography, gravure printing, etc. have been used for printing on corrugated board, but all of these printing methods involve contacting a plate or blanket with the printing medium and applying printing pressure to transfer the ink. As a result, post-printing methods are prone to uneven density due to the unevenness (flute marks) of the corrugated board surface, making post-printing particularly difficult on thick corrugated board. On the other hand, the pre-printing method solves printing problems, but the lamination process after printing takes time, and there is an issue that it is not possible to move on to the box-making process immediately after printing.

In addition, because inkjet printing is a non-contact method of recording an image on a print medium, it is easy to post-print on thick corrugated board, and the box-making process can be started immediately after printing, making it possible to meet short delivery times, so demand for inkjet printing in corrugated board printing is increasing.

When color printing is performed on cardboard base paper, white cardboard base paper is widely used. This is because good color development cannot be achieved if color ink (hereinafter sometimes referred to as "non-white ink") is printed directly on brown cardboard base paper.

On the other hand, although it is not widely used, a printing method has been devised in which white ink is printed on brown cardboard base paper and then non-white ink is applied on top of the white ink. However, printing methods using water-based inks have quality issues such as bleeding, loss of density, and repellency of the non-white ink, and do not fully meet consumer demands for high density and high resolution.

Therefore, a method has been proposed to improve color development and color reproducibility by using fluorescent ink together with non-white ink (see, for example, Patent Document 1). Also, a method has been proposed to print non-white ink on white ink with good color development (see, for example, Patent Document 2).

The present invention aims to provide a printing method that prints white ink on cardboard base paper with high water absorption and applies non-white ink on the white ink, which can prevent bleeding, density loss, and repellency of the non-white ink and achieve excellent image quality.

The printing method of the present invention as a means for solving the above-mentioned problems includes a treatment liquid applying step of applying a treatment liquid containing a polyvalent metal salt to a printing substrate having a Cobb water absorbency of 20 g/ ^m2 or more and 75 g/m2 or ^less after a contact time with water of 120 seconds, as specified in JIS-P8140; a white ink applying step of applying a white ink containing a white coloring material and water to form a white ink layer; and a non-white ink applying step of applying a non-white ink containing a non-white coloring material and water onto the white ink layer after a time of 0.5 seconds or more without providing a drying step of drying the white ink by a drying means after applying the white ink.

According to the present invention, in a printing method in which white ink is printed on cardboard base paper with high water absorption and non-white ink is applied onto the white ink, it is possible to provide a printing method that can prevent bleeding, density loss, and repellency of the non-white ink and achieve excellent image quality.

FIG. 1 is a schematic diagram showing an example of a method for printing on cardboard using a preprint method. FIG. 2 is a schematic diagram showing an example of a method for printing on cardboard using the post-printing method. FIG. 3 is a schematic diagram showing an example of a printing apparatus of the present invention used in the printing method of the present invention.

(Printing method and printing device)
The printing method of the present invention includes a treatment liquid applying step of applying a treatment liquid containing a polyvalent metal salt to a printing substrate having a Cobb water absorbency of 20 g/m2 or ^more and 75 g/m2 or ^less after a contact time with water of 120 seconds, as specified in JIS-P8140; a white ink applying step of applying a white ink containing a white coloring material and water to form a white ink layer; and a non-white ink applying step of applying a non-white ink containing a non-white coloring material and water onto the white ink layer after a time of 0.5 seconds or more without providing a drying step in which the white ink is dried by a drying means, and preferably includes a drying step, and further includes other steps as necessary.

The printing apparatus of the present invention comprises a treatment liquid applying means for applying a treatment liquid containing a polyvalent metal salt to a printing substrate having a Cobb water absorbency of 20 g/m2 or ^more and 75 g/m2 or ^less after a contact time with water of 120 seconds, as specified in JIS-P8140; a white ink applying means for applying a white ink containing a white coloring material and water to form a white ink layer; and a non-white ink applying means for applying a non-white ink containing a non-white coloring material and water onto the white ink layer after a time of 0.5 seconds or more without providing a drying step of drying the white ink by a drying means, and preferably comprises a drying means, and further comprises other means as necessary.

The printing method of the present invention can be suitably carried out by the printing device of the present invention, and the treatment liquid application step can be carried out by a treatment liquid application means, the white ink application step can be carried out by a white ink application means, the non-white ink application step can be carried out by a non-white ink application means, the drying step can be carried out by a drying means, and the other steps can be carried out by other means.

In the conventional technology described in Patent Document 1, it is difficult to eliminate the influence of the cardboard paper on the color development of non-white ink, and since fluorescent substances have poor chemical resistance and weather resistance, it cannot be said that the technology is sufficiently versatile.
In addition, in the conventional technology described in Patent Document 2, a first aggregating agent that reacts with the white particles in the white ink and a second aggregating agent that reacts with the dye in the colored ink are used in the upper and lower layers of the white ink, but this requires that the aggregating agent be supplied to the printed material multiple times, which poses a problem that the technology is not sufficiently versatile.

In the present invention, a high-quality print with little bleeding, ^low density, and repellency can be obtained by including a treatment liquid application step of applying a treatment liquid containing a polyvalent metal salt to a printed material having a Cobb water absorbency of 20 g/m2 or more and 75 g/ ^m2 or less at a contact time with water of 120 seconds as specified in JIS-P8140, a white ink application step of applying a white ink containing a white coloring material and water to form a white ink layer, and a non-white ink application step of applying a non-white ink containing a non-white coloring material and water onto the white ink layer after a time period of 0.5 seconds or more without providing a drying step of drying the white ink by a drying means after applying the white ink. That is, by applying a non-white ink onto the white ink layer after a time of 0.5 seconds or more is secured without providing a drying step of drying the white ink by a drying means, and by ensuring the time required for the polyvalent metal salt in the treatment liquid to react with the white coloring material in the white ink as an aggregating agent, it is possible to prevent bleeding (color bleeding) and a decrease in density caused by the non-white ink being mixed with the white ink. Also, by not drying the white ink layer, the white ink does not dry to form a film, and the mobility of the unreacted polyvalent metal salt diffused in the white ink is maintained, making it easy to react with the coloring material in the non-white ink, thereby preventing the repelling of the non-white ink.

<Treatment liquid application step and treatment liquid application means>
The treatment liquid application step is a step of applying a treatment liquid containing a polyvalent metal salt to a printing substrate having a Cobb water absorbency of 20 g/m2 or ^more and 75 g/ ^m2 or less after a contact time with water of 120 seconds, as specified in JIS-P8140, and is carried out by a treatment liquid application means.

<<Treatment liquid>>
The treatment liquid is applied to the substrate before the white ink is applied to the substrate. The treatment liquid is sometimes called a "pre-treatment liquid" or a "pre-coating liquid."

The treatment solution contains a polyvalent metal salt and, if necessary, other components.

The viscosity of the treatment liquid at 25°C may be adjusted in the range of 5 mPa·s to 1,000 mPa·s depending on the application method, and such a viscosity can be measured using, for example, a rotational viscometer (RE-80L, manufactured by Toki Sangyo Co., Ltd.). Measurement conditions are 25°C, a standard cone rotor (1°34' x R24), a sample liquid volume of 1.2 mL, a rotation speed of 50 rpm, and 3 minutes. If the viscosity of the treatment liquid at 25°C is 5 mPa·s to 50 mPa·s, the coating on the printed material becomes more uniform, and as a result, the ink coating is more likely to result in a uniform and even image, which is preferable.

The method of applying the treatment liquid is not particularly limited and can be appropriately selected depending on the purpose. Examples of the method include inkjet method, blade coating method, gravure coating method, gravure offset coating method, bar coating method, roll coating method, knife coating method, air knife coating method, comma coating method, U comma coating method, AKKU coating method, smoothing coating method, microgravure coating method, reverse roll coating method, four-roll coating method, five-roll coating method, dip coating method, curtain coating method, slide coating method, and die coating method. The application method can be appropriately selected depending on the material, thickness, etc. of the printed material.

The amount of the treatment liquid applied is preferably from 2 g/m ² to 30 g/m ² , and more preferably from 5 g/m ² to 20 g/m ² , in terms of solid content, relative to the substrate to be printed.

After applying the treatment liquid to the substrate, the treatment liquid layer may be dried, but it is preferable to apply the white ink onto the treatment liquid layer without drying it in terms of space and energy saving, and it is preferable to apply the white ink within 5 seconds after applying the treatment liquid to the substrate.

- Polyvalent metal salts -
The polyvalent metal salt has the function of destabilizing the dispersion of the white colorant in the white ink, and quickly aggregates the white colorant in the white ink after deposition, thereby preventing bleeding (color bleeding) and density reduction that occur when non-white inks are mixed with the white ink.

The cation in the polyvalent metal salt is not particularly limited and can be appropriately selected according to the purpose, and examples thereof include aluminum (Al(III)), calcium (Ca(II)), magnesium (Mg(II)), copper (Cu(II)), iron (Fe(II) or Fe(III)), zinc (Zn(II)), tin (Sn(II) or Sn(IV)), strontium (Sr(II)), nickel (Ni(II)), cobalt (Co (II)), barium (Ba(II)), lead (Pb(II)), zirconium (Zr(IV)), titanium (Ti(IV)), antimony (Sb(III)), bismuth (Bi(III)), tantalum (Ta(V)), arsenic (As(III)), cerium (Ce(III)), lanthanum (La(III)), yttrium (Y(III)), mercury (Hg(II)), beryllium (Be(II)), and the like ions. These may be used alone or in combination of two or more. Among these, calcium (Ca(II)) and magnesium (Mg(II)) are preferred.

The anion in the polyvalent metal salt is not particularly limited and can be appropriately selected depending on the purpose. Examples of the anion include ions of halogen elements such as fluorine (F), chlorine (Cl), bromine (Br), and iodine (I); nitrate ion (NO ₃ ⁻ ), sulfate ion (SO ₄ ²⁻ ); ions of organic carboxylic acids such as formic acid, acetic acid, lactic acid, malonic acid, oxalic acid, maleic acid, and benzoic acid; ions of organic sulfonic acids such as benzenesulfonic acid, naphtholsulfonic acid, and alkylbenzenesulfonic acid; thiocyan ion (SCN ⁻ , thiosulfate ion S ₂ O ₃ ²⁻ ), phosphate ion (PO ₄ ³⁻ ), and nitrite ion (NO ²⁻ ). These may be used alone or in combination of two or more. Among these, chloride ion (Cl ⁻ ), sulfate ion (SO ₄ ²⁻ ), and nitrate ion (NO ₃ ⁻ ) are preferred from the viewpoints of cost and safety.

The polyvalent metal salt is not particularly limited and can be appropriately selected according to the purpose. Examples of the polyvalent metal salt include aluminum chloride, calcium chloride, nickel chloride, potassium acetate, sodium acetate, calcium acetate, magnesium acetate, aluminum nitrate, magnesium nitrate, magnesium chloride, calcium nitrate, magnesium hydroxide, aluminum sulfate, magnesium sulfate, and ammonium alum. More specifically, calcium acetate monohydrate, calcium nitrate tetrahydrate, calcium chloride hexahydrate, magnesium acetate tetrahydrate, magnesium sulfate (anhydrous), aluminum nitrate nonahydrate, and nickel chloride hexahydrate can be mentioned. These may be used alone or in combination of two or more. Among these, calcium acetate monohydrate, calcium nitrate tetrahydrate, calcium chloride hexahydrate, magnesium acetate tetrahydrate, and magnesium sulfate (anhydrous) are preferred.

The content of the polyvalent metal salt is preferably 7% by mass or more, more preferably 12% by mass or more, and even more preferably 12% by mass or more to 25% by mass or less, based on the total amount of the treatment liquid. The content of the polyvalent metal salt is preferably 7% by mass or more, in order to suppress bleeding of non-white ink on white ink. In addition, the content of the polyvalent metal salt is preferably 25% by mass or less, in order to suppress the occurrence of quality defects such as precipitation, and to suppress the occurrence of quality defects such as precipitation, when the treatment liquid is stored for a long period of time.

-Other ingredients-
Examples of the other components include resins, organic solvents, water, surfactants, antifoaming agents, antiseptic and antifungal agents, rust inhibitors, and pH adjusters.

--resin--
The treatment liquid may contain a resin. The type of resin is not particularly limited, but at least one selected from the group consisting of acrylic resin, polyolefin resin, polyvinyl acetate resin, polyvinyl chloride resin, urethane resin, and copolymers thereof is preferred because it provides strong adhesion to various printing substrates.
When the resin is added to the treatment liquid, it may be added as a liquid in which resin particles are dispersed in water, or a resin commercially available as a resin emulsion may be used.
The volume average particle size of the resin particles is not particularly limited and may be appropriately selected depending on the purpose. From the viewpoint of obtaining good dispersibility, 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.).

Considering compatibility and stability when mixed with the polyvalent metal salt, the acid value of the resin is preferably 20 mg KOH/g or less.

The glass transition temperature (Tg) of the resin should be sufficient so long as it maintains adhesion to the printed material and drying properties; for example, a resin in the range of -25°C to 70°C can be suitably used. In order to prevent stickiness on the printed material surface and blocking when stacked, the resin's glass transition temperature (Tg) is preferably -25°C or higher, and in order to maintain adhesion and prevent cracking or peeling during folding in the box-making process, the Tg is preferably 70°C or lower. In particular, favorable effects can be obtained when cardboard is used as the printed material.

The content of the resin is preferably 30% by mass or less, and more preferably 0.5% by mass or more and 20% by mass or less, based on the total amount of the treatment liquid. The content refers to the mass % of the resin solid content contained in the treatment liquid. If the content is 30% by mass or less, the thickness of the resin after application of the treatment liquid does not become too thick, the occurrence of blocking and changes in the appearance of the corrugated paper are suppressed, and the effect of the polyvalent metal salt is fully exerted, which is preferable.

--Organic solvents--
The organic solvent used in the present invention is not particularly limited, and any water-soluble organic solvent can be used. Examples of the 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.
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 diol, 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, ethylene glycol monobutyl ether, diene polyhydric alcohol alkyl ethers such as ethylene 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 in the treatment liquid is not particularly limited and can be selected appropriately depending on the purpose, but taking into consideration the suitability for application to the printed material, uniform dispersion, drying properties, etc., it is preferably 5% by mass or more and 90% by mass or less, and more preferably 10% by mass or more and 70% by mass or less.

--water--
The water is not particularly limited and can be appropriately selected according to the purpose, and examples thereof include pure water such as ion-exchanged water, ultrafiltered water, reverse osmosis water, distilled water, and ultrapure water. These may be used alone or in combination of two or more. There is no particular limit to the content of water in the treatment liquid, and it is sufficient that the water content is sufficient so that the polyvalent metal salt does not precipitate during storage at room temperature.

--Surfactants--
Surfactants have the effect of lowering the surface tension of the treatment liquid, improving its wettability onto various substrates, enabling it to be applied evenly, and of distributing the polyvalent metal salt contained in the treatment liquid evenly onto the substrate.

As the surfactant, any of silicone-based surfactants, fluorine-based surfactants, amphoteric surfactants, nonionic surfactants, and anionic surfactants can be used.
Silicone surfactants are not particularly limited and can be appropriately selected according to purpose. Among them, those that do not decompose even at high pH are preferred, such as side chain modified polydimethylsiloxane, both end modified polydimethylsiloxane, one end modified polydimethylsiloxane, side chain both end modified polydimethylsiloxane, etc., and those having polyoxyethylene group or polyoxyethylene polyoxypropylene group as modified group are particularly preferred because they show good properties as aqueous surfactants. In addition, polyether modified silicone surfactants can also be used as the silicone surfactant, such as a compound in which a polyalkylene oxide structure is introduced into the Si part side chain of dimethylpolysiloxane.

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. are included.As the perfluoroalkyl carboxylic acid compound, for example, perfluoroalkyl carboxylic acid, perfluoroalkyl carboxylate, etc. are included.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. are included. Counter ions of the salts in these fluorosurfactants include Li, _Na , K, _NH4 , _NH3CH2CH2OH , _NH2 ( _{CH2CH2OH ) 2} , _NH ( _CH2CH2OH ) ₃ , and _the like.
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 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. Among these, polyether-modified silicone surfactants having a polyoxyethylene group or a polyoxyethylene polyoxypropylene group as a modifying group are particularly preferred because they exhibit good properties as an aqueous surfactant.
Such surfactants may be appropriately synthesized or 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 one in which a polyalkylene oxide structure is introduced into the Si side chain of dimethylpolysiloxane, as represented by the general formula (S-1).

（但し、前記一般式（Ｓ－１）式中、ｍ、ｎ、ａ、及びｂは、それぞれ独立に、整数を表し、Ｒは、アルキレン基を表し、Ｒ’は、アルキル基を表す。）

(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, such as KF-618, KF-642, KF-643 (all manufactured by Shin-Etsu Chemical Co., Ltd.), EMALEX-SS-5602, SS-1906EX (all manufactured by Nippon Emulsion Co., Ltd.), FZ-2105, FZ-2118, FZ-2154, FZ-2161, FZ-2162, FZ-2163, FZ-2164 (all manufactured by Dow Corning Toray Silicone Co., Ltd.), BYK-33, BYK-387 (all manufactured by BYK-Chemie Co., Ltd.), TSF4440, TSF4452, TSF4453 (all manufactured by Toshiba Silicon Co., Ltd.), etc.

The fluorine-based surfactant is preferably a compound having 2 to 16 fluorine-substituted carbon atoms, and more preferably a compound having 4 to 16 fluorine-substituted carbon atoms.
Examples of the fluorine-based surfactant include perfluoroalkyl phosphate compounds, perfluoroalkyl ethylene oxide adducts, and polyoxyalkylene ether polymer compounds having perfluoroalkyl ether groups on the side chains.
Among these, polyoxyalkylene ether polymer compounds having a perfluoroalkyl ether group in the side chain are preferred because they have little foaming property, and in particular, fluorine-based surfactants represented by any one of the following general formulas (F-1) and (F-2) are preferred.

上記一般式（Ｆ－１）で表される化合物において、水溶性を付与するためにｍは０～１０の整数が好ましく、ｎは０～４０の整数が好ましい。

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.

[General formula (F-2)]
C _n F _2n+ -CH ₂ CH(OH)CH ₂ -O-(CH ₂ CH ₂ O) _a -Y
In the compound represented by the above general formula (F-2), Y is H, or C _m F _2m+1 where m is an integer from 1 to 6, or CH ₂ CH(OH)CH ₂ -C _m F _2m+1 where m is an integer from 4 to 6, or C _p H _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 fluorosurfactant, commercially available products may be used. Examples of such 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); Megaf FAC F-470, F-1405, F-474 (all manufactured by DIC Corporation); 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 having good print quality, particularly color development and penetration into paper. From the viewpoint of significantly improving the dyeability, wettability, and dye uniformity, FS-3100, FS-34, and FS-300 manufactured by Chemours, FT-110, FT-250, FT-251, FT-400S, FT-150, and FT-400SW manufactured by Neos Co., Ltd., Polyfox PF-151N manufactured by Omnova, and Unidyne DSN-403N manufactured by Daikin Industries, Ltd. are particularly preferred.

The content of the surfactant is not particularly limited and can be appropriately selected depending on the purpose, but from the viewpoint of excellent wettability and ejection stability and improved image quality, it 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.

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

--Anti-septic and anti-fungal agent--
The antiseptic and antifungal agent is not particularly limited, and examples thereof include 1,2-benzisothiazolin-3-one.

--Rust inhibitor--
The rust inhibitor is not particularly limited, and examples thereof include acid sulfite and sodium thiosulfate.

--pH adjuster--
The treatment liquid in the present invention may contain a pH adjuster. The pH adjuster is not particularly limited, and examples thereof include amines such as diethanolamine and triethanolamine. The pH of the treatment liquid is preferably 7 to 12, more preferably 8 to 11, from the viewpoint of preventing corrosion of metal members that come into contact with the liquid.

<<Printed material>>
By applying the treatment liquid of the present invention, a printed matter having excellent color density and excellent bleed resistance can be obtained on a printed material having a Cobb water absorbency of 20 g/m2 or ^more and 75 g/ ^m2 or less at a contact time with water of 120 seconds as specified in JIS-P 8140. Even when cardboard (liner paper) is used as the printed material, a printed matter having excellent color density and excellent bleed resistance can be obtained.

Here, printing methods for cardboard can be broadly divided into a method (preprint method) in which an image 11 is recorded with printing ink on cardboard base paper (surface liner paper 10) as shown in Figure 1, and then a core 12 and a back liner paper 13 are laminated using a corrugator machine to produce cardboard, and a method (postprint method) in which an image 11 is recorded with printing ink on the surface liner paper 10 of the already laminated cardboard as shown in Figure 2, and the present invention can be suitably used for either method.
The preprint method is preferably used because the surface liner paper can be wound into a roll, so that the substrate to be printed is a continuous paper, and printing can be performed using a printing machine for continuous paper. The postprint method is preferably used because the substrate to be printed is easy to store, and furthermore, it can be delivered directly to the customer after printing.

Corrugated cardboard is basically composed of three sheets of paper: a surface liner paper, a core, and a back liner paper. The strength can be adjusted by changing the materials of the surface liner paper, the core, and the back liner paper. The core comes in different wave heights, with the basic ones being 5mm and 3mm. There are also "double-sided corrugated cardboard" which has multiple cores stacked together, for example a five-ply structure, and can be used as the printing material in the present invention.
The present invention is suitable for printing on the front liner paper in both the preprinting method and the postprinting method. It is also possible to print on the back liner paper and print on double-sided printed corrugated board.

Examples of fiber materials used in the manufacture of liner paper include bleached hardwood or softwood kraft pulp, unbleached hardwood or softwood kraft pulp, and sulfite hardwood or softwood pulp. In addition, chemically treated pulp, pulp chemically treated using kenaf, hemp, reed, etc., virgin pulp such as ground pulp, chemi-ground pulp, and semi-chemical pulp, and recycled paper such as cardboard, newspapers, magazines, and flyers can also be used.

The cardboard base paper (liner paper) has a Cobb water absorbency of 20 g/m2 or more and 75 g/m2 or ^less , preferably 23 g/ ^m2 or more and 69 g/ ^m2 or ^less , and more preferably 35 g/m2 or ^more and 60 g/ ^m2 or less, as specified in JIS-P8140, after a contact time with water of 120 seconds. When the Cobb water absorbency is 20 g/ ^m2 or more, the white ink can be adequately spread and is less likely to be repelled by the surface. When the Cobb water absorbency is 75 g/ ^m2 or less, the white ink has good fixability and can be prevented from bleeding.
The Cobb water absorbency is the Cobb water absorbency after a contact time with water of 120 seconds, as specified in JIS-P8140, and can be measured, for example, by setting a cylinder on a cardboard base paper (test piece) having a contact area with water of 100 ^cm2 , pouring 100 mL of water into the base paper while the base paper and the cylinder are clamped together to prevent water leakage, discarding the water after a contact time of 120 seconds, quickly removing excess water on the base paper with blotting paper, and weighing the change in weight of the base paper.

The basis weight of the cardboard base paper (liner paper) is preferably 100 g/ ^m2 or more and 400 g/ ^m2 or less, and from the viewpoint of suitability for lamination by a corrugator machine, more preferably 150 g/ ^m2 or more and 300 g/ ^m2 or less.

The lightness L ^* value of the printed material is preferably 60 or less, and more preferably 55 or less.
When the lightness L ^* value is 60 or less, the difference in lightness between the white ink printed area and the non-printed area increases, which has the advantage of improving the visibility of the white ink.
The lightness L ^* value can be measured, for example, by using a spectrophotometric densitometer (device name: X-Rite 939, manufactured by X-Rite Corporation).

<White ink application step and white ink application unit>
The white ink applying step is a step of applying a white ink containing a white coloring material and water to form a white ink layer, and is carried out by a white ink applying unit.

The method for applying the white ink is not particularly limited, and examples thereof include an inkjet method, a blade coating method, a gravure coating method, a gravure offset coating method, a bar coating method, a roll coating method, a knife coating method, an air knife coating method, a comma coating method, a U comma coating method, an AKKU coating method, a smoothing coating method, a microgravure coating method, a reverse roll coating method, a four-roll coating method, a five-roll coating method, a dip coating method, a curtain coating method, a slide coating method, a die coating method, etc. Among these, the inkjet method is preferably used.
In the white ink application step, it is preferable to apply the white ink two or more times from the viewpoint of improving the concealing property.
From the viewpoint of improving the concealing property, the amount of white ink applied when forming a solid image is preferably 5 g/m2 or ^more and 25 g/m2 ^or less, more preferably 10 g/ ^m2 or more and 25 g/m2 or ^less , and even more preferably 11 g/m2 or ^more and 22 g/ ^m2 or less.

<<White ink>>
The white ink contains a white colorant and water, and further contains other components as necessary.

- White color material -
The standard for the whiteness of white ink is ISO-2469 (JIS-8148), and generally, inks with a whiteness of 70 or higher are used as white coloring materials.
The coloring material used in the white ink is preferably a metal oxide, such as titanium oxide, iron oxide, tin oxide, zirconium oxide, iron titanate (a composite oxide of iron and titanium), etc. White particles having a hollow structure are also preferably used.
Examples of white particles having a hollow structure used in white ink include hollow resin particles and inorganic hollow particles.
Examples of the resin composition of the hollow resin particles include acrylic resins such as acrylic resin, styrene-acrylic resin, and crosslinked styrene-acrylic resin, urethane resin, and maleic resin.
Examples of materials for the inorganic hollow particles include white oxides, nitrides, and oxynitrides of metals such as silicon, aluminum, titanium, strontium, and zirconium, various types of glass, and inorganic compounds such as silica.
As a coloring material for use in white ink, when a metal oxide is used, it is superior in that it increases the whiteness, and when white particles having a hollow structure are used, it is superior in that it is less likely to settle out and therefore has excellent sedimentation properties.

The content of the white colorant in the white ink is preferably 0.1% by mass or more and 15% by mass or less, and more preferably 1% by mass or more and 10% by mass or less.

Methods for dispersing a pigment to obtain an ink include a method in which a hydrophilic functional group is introduced into the pigment to make it a self-dispersing pigment, a method in which the surface of the pigment is coated with a resin and then dispersed, and a method in which a dispersant is used to disperse the pigment.
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, there is a method in which the pigment is encapsulated in a microcapsule to make it dispersible in water. This can be called a resin-coated pigment. In this case, it is not necessary for all of the pigments blended in the ink to be coated with a resin, and uncoated or partially coated pigments may be dispersed in the ink as long as the effect of the present invention is not impaired.
Examples of the method for dispersing using a dispersant include a method for dispersing using a known low molecular weight dispersant or a polymeric dispersant, typified by a surfactant.
As the dispersant, for example, anionic surfactants, cationic surfactants, amphoteric surfactants, nonionic surfactants, etc. can be used depending on the pigment.
As the dispersant, RT-100 (nonionic surfactant) manufactured by Takemoto Oil Co., Ltd. and sodium naphthalenesulfonate formalin condensate can also be suitably used.
The dispersants may be used alone or in combination of two or more.

- Pigment dispersion -
It is possible to obtain ink by mixing the pigment with materials such as water and organic solvents. It is also possible to manufacture ink by mixing the pigment with other materials such as water and dispersants to prepare a pigment dispersion, and then mixing the pigment with materials such as water and organic solvents.
The pigment dispersion is obtained by mixing and dispersing water, a pigment, a pigment dispersant, and other components as necessary, and adjusting the particle size. Dispersion is preferably performed using a dispersing machine.
Although there is no particular restriction on the particle size of the pigment in the pigment dispersion, the maximum frequency in terms of the maximum number is preferably 20 nm or more and 500 nm or less, and more preferably 20 nm or more and 150 nm or less, in order to improve the dispersion stability of the pigment and the image quality such as ejection stability and image density. The particle size of the pigment can be measured using a particle size analyzer (Nanotrac Wave-UT151, manufactured by Microtrac Bell Co., Ltd.).
The content of the pigment in the pigment dispersion is not particularly limited and can be appropriately selected depending on the purpose. From the viewpoints of obtaining good ejection stability and increasing image density, the content is preferably 0.1% by mass or more and 50% by mass or less, and more preferably 0.1% by mass or more and 30% by mass or less.
It is preferable to filter out coarse particles from the pigment dispersion using a filter or a centrifugal separator, and degas the pigment dispersion, if necessary.

-water-
The water is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include pure water such as ion-exchanged water, ultrafiltered water, reverse osmosis water, distilled water, and ultrapure water, etc. These may be used alone or in combination of two or more kinds.
The water content in the white ink is not particularly limited and can be appropriately selected depending on the purpose. From the viewpoints of the drying property and ejection reliability of the ink, however, the water content is preferably from 10% by mass to 90% by mass, and more preferably from 20% by mass to 60% by mass.

-Other ingredients-
Examples of the other components include resins, organic solvents, surfactants, antifoaming agents, antiseptic and antifungal agents, rust inhibitors, and pH adjusters.

-resin-
The type of resin contained in the ink is not particularly limited and can be appropriately selected depending on the purpose. Examples of the resin 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 to form a resin emulsion, and the resin particles may be 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 kinds 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, by 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, based on the total amount of ink.

There are no particular restrictions on the particle size of the solids in the ink, and they can be selected appropriately depending on the purpose, but in terms of improving image quality such as ejection stability and image density, the maximum frequency in terms of maximum number is preferably 20 nm or more and 1,000 nm or less, and more preferably 20 nm or more and 150 nm or less. The solids include resin particles, pigment particles, etc. The particle size can be measured using a particle size analyzer (Nanotrac Wave-UT151, manufactured by Microtrac Bell Co., Ltd.).

There are no particular limitations on the organic solvent, surfactant, defoamer, antiseptic/fungal agent, rust inhibitor, and pH adjuster, and they can be appropriately selected depending on the purpose. For example, the same organic solvent, surfactant, defoamer, antiseptic/fungal agent, rust inhibitor, and pH adjuster as those contained in the treatment liquid can be used.

The white ink can be prepared by dispersing or dissolving each of the components in, for example, water as a solvent, and further mixing the components by stirring as necessary.
For the stirring and mixing, for example, a stirrer using a normal stirring blade, a magnetic stirrer, a high-speed disperser, or the like can be used.

The physical properties of the white 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 white ink at 25° C. is preferably from 5 mPa·s to 30 mPa·s, more preferably from 5 mPa·s to 25 mPa·s, in order to improve the print density and character quality and to obtain 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 surface tension of the white ink is preferably 35 mN/m or less, and more preferably 32 mN/m or less at 25° C., in order to ensure that the ink is appropriately leveled on the substrate and the drying time of the ink is shortened.
The pH of the white ink is preferably from 7 to 12, and more preferably from 8 to 11, from the viewpoint of preventing corrosion of metal members that come into contact with the ink.

<Non-white ink application step and non-white ink application unit>
The non-white ink applying step is a step of applying a non-white ink containing a non-white colorant and water onto the white ink layer after a time period of 0.5 seconds or more without a drying step of drying the white ink by a drying means, and can be performed by a non-white ink applying means.

The method for applying the non-white ink is not particularly limited, and examples thereof include an inkjet method, a blade coating method, a gravure coating method, a gravure offset coating method, a bar coating method, a roll coating method, a knife coating method, an air knife coating method, a comma coating method, a U comma coating method, an AKKU coating method, a smoothing coating method, a microgravure coating method, a reverse roll coating method, a four-roll coating method, a five-roll coating method, a dip coating method, a curtain coating method, a slide coating method, a die coating method, etc. Among these, the inkjet method is preferably used.
In order to realize a high image density, the amount of non-white ink applied when creating a solid image is preferably 5 g/m ² or more and 15 g/m ² or less, and more preferably 7 g/m ² or more and 15 g/m ² or less.

The time period between application of the white ink and application of the non-white ink must be at least 0.5 seconds, is preferably at least 1 second, is more preferably from 1 to 4 seconds, and is even more preferably from 2 to 4 seconds.
When the time between the application of the white ink and the application of the non-white ink is 0.5 seconds or longer, the time required for the polyvalent metal salt in the treatment liquid to react as a coagulant with the white colorant in the white ink can be secured, and bleeding (color bleeding) and a decrease in density caused by the mixing of the non-white ink with the white ink can be prevented.
Here, "the time from application of white ink to application of non-white ink" means the time from when the white ink is applied (lands) on the printed substrate to when the non-white ink is applied (lands) on the printed substrate, and can be measured, for example, by dividing the distance [m] between the landing position of the white ink and the landing position of the non-white ink on the printing press by the conveying speed [m/sec] of the printed substrate, or by directly measuring the time from when the white ink lands to when the non-white ink lands using a measuring device such as a stopwatch or a timer with a sensor.

<<Non-white ink>>
The non-white ink contains a non-white colorant and water, and further contains other components as required.

-Non-white coloring materials-
Examples of non-white inks include color inks, black inks, gray inks, clear inks, and metallic inks.
Examples of the color ink include cyan ink, magenta ink, yellow ink, light cyan ink, light magenta ink, red ink, green ink, blue ink, orange ink, and violet ink.
The coloring material used in the non-white ink is not particularly limited as long as it exhibits a non-white color and can be appropriately selected depending on the purpose, and examples of the coloring material include dyes and pigments. These may be used alone or in combination of two or more kinds. Among these, pigments are preferred.
Examples of the pigment include inorganic pigments and organic pigments.

Examples of the inorganic pigments include calcium carbonate, barium sulfate, aluminum hydroxide, barium yellow, cadmium red, chrome yellow, and carbon black produced by known methods such as the contact method, furnace method, and thermal method. These may be used alone or in combination of two or more types.

Examples of the organic pigment include azo pigments (including, for example, azo lakes, insoluble azo pigments, condensed azo pigments, chelate azo pigments, etc.), polycyclic pigments (for example, phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, indigo pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments, etc.), dye chelates (for example, basic dye type chelates, acid dye type chelates, etc.), nitro pigments, nitroso pigments, aniline black, etc. These may be used alone or in combination of two or more.
Of these pigments, those having good affinity with the solvent are preferably used.

Examples of the pigments for black include carbon blacks (C.I. Pigment Black 7) such as furnace black, lamp black, acetylene black, and channel black, and organic pigments such as copper, iron (C.I. Pigment Black 11), and aniline black (C.I. Pigment Black 1). These may be used alone or in combination of two or more.

For color, for example, 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; 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 (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 ocher), 104, 105, 106, 108 (Cadmium Red), 112, 114, 122 (Quinacridone Magenta), 123, 146, 149, 166, 168, 170, 172, 177, 178, 179, 185, 190, 193, 209, 219; C.I. Examples of the pigments include 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 (Phthalocyanine Blue), 16, 17:1, 56, 60, 63; C.I. Pigment Green 1, 4, 7, 8, 10, 17, 18, 36, etc. These may be used alone or in combination of two or more.

Examples of the dyes 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, 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, etc. These may be used alone or in combination of two or more.

The coloring material used in metallic ink is, for example, a fine powder made by finely grinding a metal element, an alloy, or a metal compound. Specific examples include a material made of one or more of the group of metal elements consisting of aluminum, silver, gold, nickel, chromium, tin, zinc, indium, titanium, silicon, copper, and platinum, or an alloy. Examples of the metal compound include one or more of the oxides, nitrides, sulfides, and carbides of the metal element or alloy.

The content of non-white colorant in the non-white ink is preferably 0.1% by mass or more and 15% by mass or less, and more preferably 1% by mass or more and 10% by mass or less.

-water-
The water is not particularly limited and can be appropriately selected depending on the purpose. For example, the same water as that contained in the white ink can be used.

-Other ingredients-
Examples of the other components include resins, organic solvents, surfactants, antifoaming agents, antiseptic and antifungal agents, rust inhibitors, and pH adjusters.

The resin is not particularly limited and can be appropriately selected depending on the purpose. For example, the same resin as that contained in the white ink can be used.
The organic solvent, the surfactant, the defoaming agent, the antiseptic/antifungal agent, the rust inhibitor, and the pH adjuster are not particularly limited and can be appropriately selected depending on the purpose. For example, they are the same as those in the above-mentioned treatment liquid, so description of these will be omitted.

<Drying step and drying means>
In the present invention, after applying a pretreatment liquid to a printing substrate, the printing substrate to which the pretreatment liquid has been applied is dried, then white ink is applied, and after the application of the white ink, a non-white ink is applied after a time period of 0.5 seconds or more without providing a drying step of drying by a drying means. After the non-white ink is applied, the printing substrate to which the white ink and non-white ink have been applied is dried. Alternatively, after applying a pretreatment liquid to a printing substrate, the printing substrate to which the pretreatment liquid has been applied is not dried, then white ink is applied, and after the application of the white ink, a non-white ink is applied after a time period of 0.5 seconds or more without providing a drying step of drying by a drying means. After the non-white ink is applied, the printing substrate to which the white ink and non-white ink have been applied is dried.

After the white ink is applied, a non-white ink is applied without providing a drying step in which the ink is dried using a drying means. The drying means referred to here includes, for example, a roll heater, a drum heater, a hot air drying device, an infrared drying device, an ultraviolet drying device, etc., which are drying means other than natural drying. After the white ink is applied and before the non-white ink is applied, it is sufficient that a drying step using a drying means is not provided, and natural drying is not excluded.
After the white ink is applied, a drying step is not performed using a drying means, and a non-white ink is applied after a delay of 0.5 seconds or more. In this case, the delay of 0.5 seconds or more is preferably performed at a temperature of 0° C. to 50° C., and more preferably at a temperature of 15° C. to 40° C., for 0.5 seconds or more.
After the white ink is applied, a time period of 0.5 seconds or more is allowed to elapse before the non-white ink is applied, preferably 1 second or more, more preferably 1 second to 4 seconds, and even more preferably 2 seconds to 4 seconds.
The drying step of drying the printing substrate to which the non-white ink has been applied is carried out by a drying means.

Drying of the printed material to which non-white ink has been applied is a process in which the printed material (cardboard base paper) is heated and dried using known methods such as a roll heater, drum heater, hot air dryer, infrared dryer, or ultraviolet dryer. It is preferable to bring the surface temperature of the printed material to 60°C or higher, preferably 60°C or higher and 100°C or lower. The drying time is preferably 1 second or longer and less than 300 seconds.

(Printed matter)
The printed matter of the present invention has a treatment liquid layer containing a polyvalent metal salt, a white ink layer containing a white coloring material, and a non-white ink layer containing a non-white coloring material on a printed matter having a Cobb water absorbency of 20 g/m2 or ^more and 75 g/m2 or ^less after a contact time with water of 120 seconds, as specified in JIS-P8140.
As the printing material, cardboard base paper can be suitably used.
The printed matter has an image formed on a substrate using the non-white ink used in the present invention.
A printed matter can be produced by printing using the printing device and printing method of the present invention.
The printing device does not have to be a device dedicated to printing on cardboard; an inkjet printing device can be used.

<Printing device and printing method>
Fig. 3 is a schematic diagram showing an example of a printing apparatus used in the printing method of the present invention. The printing apparatus 100 in Fig. 3 has a treatment liquid application device 2 that applies a treatment liquid, a white ink ejection head 3 that ejects white ink (W), a non-white ink (color ink) ejection head 4 that ejects black ink (K), cyan ink (C), magenta ink (M) and yellow ink (Y), a first drying device 5, a second drying device 6, and a transport belt 5 that transports the printing substrate 1.
3, the first drying device 5 is installed between the treatment liquid application device 2 and the white ink ejection head 3 as necessary, and even when the first drying device 5 is installed, it is not necessary to dry the applied treatment liquid. The second drying device 6 is installed behind the yellow ink (Y) ejection head of the non-white ink (color ink) ejection heads 4, and drying the non-white ink is preferable in terms of preventing the non-white ink from rubbing and sticking to the back.
As described above, since the non-white ink is applied after a time of 0.5 seconds or more is elapsed without providing a drying step in which the white ink is dried by a drying means after the white ink is applied to the printing substrate, it is necessary to provide an appropriate distance between the white ink ejection head 3 and the color ink ejection head 4 in Fig. 3. For example, when printing is performed at a speed of 60 meters per minute, in order to ensure a time of 0.5 seconds or more, it is preferable to separate the white ink ejection head 3 and the color ink ejection head 4 by about 0.5 meters or more, and similarly, in order to ensure a time of 2 seconds or more, it is preferable to separate the white ink ejection head 3 and the color ink ejection head 4 by about 2.0 meters or more. It is also possible to integrate the white ink ejection head 3 and the color ink ejection head 4 into an ejection head that can be moved to a desired ejection position.
In FIG. 3, two or more white ink ejection heads 3 may be arranged in series to stack two or more layers of white ink, in which case better white ink hiding power can be obtained.

The recording apparatus and the recording method may have a heating means used in the heating step and a drying means used in the drying step. The heating means and the drying means include, for example, a means for heating and drying the printed surface or the back surface of the printed material. The heating means and the drying means are not particularly limited, but for example, a hot air heater or an infrared heater can be used. Heating and drying can be performed before, during, or after printing.
Furthermore, the recording device and recording method are not limited to those that visualize meaningful images such as characters and figures with ink. For example, those that form patterns such as geometric designs and those that form three-dimensional images are also included.
Furthermore, unless otherwise specified, the recording apparatus includes both a serial type apparatus in which the ejection head moves and a line type apparatus in which the ejection head does not move.
Furthermore, this recording device includes not only desktop types, but also wide-width recording devices that can print on A0-sized substrates, and continuous-feed printers that can use continuous paper wound into a roll as the substrate.

In the present invention, the terms image formation, recording, printing, printing, etc. are all synonymous.
Recording medium, media, and printed material are all synonymous.

The following describes examples of the present invention, but the present invention is not limited to these examples. Unless otherwise specified, the preparation and evaluation of the examples and comparative examples were carried out under conditions of 25°C and a relative humidity of 60%.

(Preparation Example 1 of White Pigment Dispersion)
--Preparation of White Pigment Dispersion 1--
A mixture having the following composition was premixed, and then circulated and dispersed for 7 hours in a disk-type bead mill (manufactured by Shinmaru Enterprises, KDL model, media: zirconia balls with a diameter of 0.3 mm) to obtain white pigment dispersion 1 (pigment concentration: 40% by mass).
[Formulation of White Pigment Dispersion 1]
C.I. Pigment White 7 (manufactured by Ishihara Sangyo Kaisha, Ltd.): 40 parts by mass Acrylic polymer dispersant (Disperbyk-2015, manufactured by BYK Japan Co., Ltd.): 5 parts by mass Ion-exchanged water: 55 parts by mass

(Preparation Example 1 of Non-White Pigment Dispersion)
--Preparation of Magenta Pigment Dispersion 1--
A mixture having the following formulation was premixed and then circulated and dispersed for 7 hours in a disk-type bead mill (KDL type, manufactured by Shinmaru Enterprises, media: zirconia balls with a diameter of 0.3 mm) to obtain Magenta Pigment Dispersion 1 (pigment concentration: 15% by mass).
[Formulation of Magenta Pigment Dispersion 1]
C.I. Pigment Red 269 (manufactured by Clariant): 15 parts by mass Acrylic polymer dispersant (Disperbyk-2010, manufactured by BYK Japan Co., Ltd.): 5 parts by mass Ion-exchanged water: 80 parts by mass

(White Ink Production Example 1)
--Preparation of White Ink 1--
A mixture having the following formulation for white ink 1 was premixed, and then stirred at 2,000 rpm for 10 minutes using a dissolver (DISPERMAT LC30, manufactured by Eiko Seiki Co., Ltd.), and then filtered through a polypropylene filter having an average pore size of 0.8 μm, thereby obtaining white ink 1.
[White ink 1 formulation]
White pigment dispersion 1: 30 parts by mass TEGO (registered trademark) WET 270 (silicone-based surfactant, manufactured by Evonik): 1 part by mass Proxel LV (antiseptic and antifungal agent, manufactured by Avecia): 0.1 part by mass 1,2-propanediol: 25 parts by mass Propylene glycol monomethyl ether acetate: 5 parts by mass Ion-exchanged water: 38.9 parts by mass

(Non-white ink production example 1)
--Preparation of Magenta Ink 1--
The mixture of the following formulation for magenta ink 1 was premixed, and then stirred at 2,000 rpm for 10 minutes using a dissolver (DISPERMAT LC30, manufactured by Eiko Seiki Co., Ltd.), and then filtered through a polypropylene filter having an average pore size of 0.8 μm, thereby obtaining magenta ink 1.
[Magenta Ink 1 Formulation]
Magenta pigment dispersion 1: 30 parts by mass TEGO (registered trademark) WET 270 (silicone-based surfactant, manufactured by Evonik): 1 part by mass Proxel LV (antiseptic and antifungal agent, manufactured by Avecia): 0.1 part by mass 1,2-propanediol: 25 parts by mass Propylene glycol monomethyl ether acetate: 5 parts by mass Ion-exchanged water: 38.9 parts by mass

(Preparation Example 1 of Processing Solution)
--Preparation of Processing Solution 1--
The mixture of the following formulation for treatment liquid 1 was premixed, and then stirred at 2,000 rpm for 10 minutes using a dissolver (DISPERMAT LC30, manufactured by Eiko Seiki Co., Ltd.) to obtain treatment liquid 1. The viscosity of treatment liquid 1 at 25° C. was 7.0 mPa·s.
[Formulation of treatment liquid 1]
・1,2-propanediol: 10.0 parts by mass ・3-methoxybutanol: 10.0 parts by mass ・TEGO (registered trademark) WET 270 (silicone-based surfactant, manufactured by Evonik): 0.5 parts by mass ・Proxel LV (manufactured by Avecia, antiseptic and antifungal agent): 0.1 parts by mass ・Magnesium acetate tetrahydrate: 12.0 parts by mass ・Ion-exchanged water: 67.4 parts by mass

(Preparation Example 2 of Processing Solution)
--Preparation of Processing Solution 2--
The mixture of the following formulation for treatment liquid 2 was premixed, and then stirred at 2,000 rpm for 10 minutes using a dissolver (DISPERMAT LC30, manufactured by Eiko Seiki Co., Ltd.) to obtain treatment liquid 2. The viscosity of treatment liquid 2 at 25° C. was 6.8 mPa·s.
[Formulation of treatment liquid 2]
・1,2-propanediol: 10.0 parts by mass ・3-methoxybutanol: 10.0 parts by mass ・TEGO (registered trademark) WET 270 (silicone-based surfactant, manufactured by Evonik): 0.5 parts by mass ・Proxel LV (manufactured by Avecia, antiseptic and antifungal agent): 0.1 parts by mass ・Magnesium acetate tetrahydrate: 6.0 parts by mass ・Ion-exchanged water: 73.4 parts by mass

(Examples 1 to 10 and Comparative Examples 1 to 5)
<Processing Liquid Application Step>
NPK liner TF (rice weight 170 g/ ^m2 , brown cardboard base paper, Cobb water absorbency 55 g/ ^m2 , brightness L ^* value 51, manufactured by Nippon Paper Industries Co., Ltd.) was used as the printing substrate, and the treatment liquid 1 or the treatment liquid 2 was applied onto the printing substrate using a bar coater. The Cobb water absorbency is a value measured after a contact time with water of 120 seconds as specified in JIS-P8140. The coating amount of the treatment liquid was 10 g/ ^m2 .
After application of the treatment liquid, in the condition where the treatment liquid was dried, the treatment liquid was dried for 2 minutes in a dryer set at 80° C. On the other hand, in the condition where the treatment liquid was not dried, white ink was printed 5 seconds after application of the treatment liquid.

<White Ink Application Step>
The white ink 1 was filled into an inkjet discharge head (MH5421MF, manufactured by Ricoh Co., Ltd.), and a solid image having a width of 5 cm and a length of 20 cm was formed at 600 dpi on the printing substrate coated with the treatment liquid. The printing substrate was placed on a conveyor device and passed directly under the inkjet discharge head at a speed of 48 meters per minute, thereby printing with the white ink 1. The amount of the white ink 1 applied was 11 g/ ^m2 .
When printing the white ink 1 twice in succession, two of the inkjet ejection heads were connected to perform printing, and the amount of the white ink 1 applied in this case was 22 g/m ² .
After printing, in the condition where the white ink 1 was dried, it was dried for 2 minutes in a dryer set at 80° C. In the condition where the white ink 1 was not dried, after the white ink 1 was printed, the magenta ink 1 was printed continuously after the number of seconds shown in Tables 1 to 3.

<Step of applying non-white ink>
The magenta ink 1 was filled into an inkjet discharge head (MH5421MF, manufactured by Ricoh Co., Ltd.), and a solid image having a width of 4 cm and a length of 10 cm was formed at 600 dpi directly above the white ink 1 printed on the printing substrate. The inkjet discharge head filled with the magenta ink 1 was installed behind the inkjet discharge head filled with the white ink 1 on the conveyor device at a distance such that the time from printing the white ink 1 to consecutively printing the magenta ink 1 was the number of seconds shown in Tables 1 to 3. In Example 1, the distance between the inkjet discharge head filled with the white ink 1 and the inkjet discharge head filled with the magenta ink 1 was 1.6 meters.

<Printed material drying process>
After printing with the magenta ink 1, the printed material was dried in a dryer set at 80° C. for 2 minutes.

Next, the "concealment power of white ink," "bleeding of magenta ink on white ink," "density of magenta ink on white ink," and "repellency of magenta ink on white ink" were evaluated as follows. The results are shown in Tables 1 to 3.

<Evaluation of the hiding power of white ink>
Ten sheets of Ricopy PPC paper type 6200 (manufactured by Ricoh Co., Ltd.) were placed under each of the printed materials in the combinations shown in Tables 1 to 3 as backing during color measurement, and a spectrophotometric densitometer (device name: X-Rite 939, manufactured by X-Rite Co., Ltd.) was used to measure the lightness (L ^* value) at any five points in a solid image printed with only white ink, and the average value was evaluated according to the following criteria. A score of ◯ or higher is a level that can be actually used.
[Evaluation Criteria]
◎: Lightness (L ^* value) is 80 or more. ◯: Lightness (L ^* value) is 75 or more and less than 80. △: Lightness (L ^* value) is 70 or more and less than 75. ×: Lightness (L ^* value) is less than 70.

<Evaluation of bleeding of magenta ink on white ink>
The edges of the magenta ink solid image formed on the white ink were visually observed to measure the distance of the magenta ink solid image portion that had seeped into the white ink solid image of each printed substrate for the combinations shown in Tables 1 to 3, and the results were evaluated according to the following criteria.
[Evaluation Criteria]
◎: Almost no bleeding is observed. ◯: Bleeding is observed with a bleeding distance of less than 0.5 mm. △: Bleeding is observed with a bleeding distance of 0.5 mm or more and less than 1 mm. ×: Bleeding is observed with a bleeding distance of 1 mm or more.

<Evaluation of Magenta Ink Density on White Ink>
Ten sheets of Ricopy PPC paper type 6200 (manufactured by Ricoh Co., Ltd.) were placed under each of the printed materials in the combinations shown in Tables 1 to 3 as backing during color measurement, and a spectrophotometric densitometer (device name: X-Rite 939, manufactured by X-Rite) was used to measure the optical density (magenta) at any five points in a solid image in which magenta ink was printed on white ink, and the average value was evaluated according to the following criteria. Note that a score of △ or higher is a level that can be actually used.
[Evaluation Criteria]
◯: Optical density (magenta) is 1.5 or more △: Optical density (magenta) is 1.2 or more and less than 1.5 ×: Optical density (magenta) is less than 1.2

<Evaluation of Magenta Ink Repelling on White Ink>
The solid magenta ink image formed on the white ink was visually observed and the degree of repellency of the solid magenta ink image portion on the solid white ink image of each printed material in the combinations shown in Tables 1 to 3 was evaluated according to the following criteria. A score of ◯ or higher is a practically usable level.
[Evaluation Criteria]
◎: No repelling of magenta ink is observed, and there is no unevenness. ○: No repelling of magenta ink is observed, but unevenness is visible. △: White ink underneath the magenta ink is slightly exposed. ×: White ink underneath the magenta ink is clearly exposed.

From the results in Tables 1 to 3, it was found that Examples 1 to 10 all had better evaluation results in terms of "concealment ability of white ink,""bleeding of magenta ink on white ink,""density of magenta ink on white ink," and "repellency of magenta ink on white ink," compared to Comparative Examples 1 to 5.
In contrast, in Comparative Examples 1 to 3, the white ink layer was dried, resulting in "magenta ink bleeding on the white ink" and "repelling of magenta ink on the white ink." This is believed to be due to the effect that the mobility of unreacted polyvalent metal salts that had diffused into the white ink was suppressed by the drying of the white ink, reducing their reactivity with the coloring material (pigment) in the magenta ink. In addition, the decrease in "magenta ink concentration on the white ink" is believed to be due to the effect of reduced ink receptivity of the magenta ink layer caused by the repelling.
In addition, in Comparative Examples 4 and 5, the time from application of the white ink to successive printing of the magenta ink was less than 0.5 seconds, and "bleeding of the magenta ink on the white ink" occurred.
Furthermore, a decrease in the "density of magenta ink on white ink" occurred in Comparative Example 4. This is believed to be due to the effect of the magenta ink being mixed with the white ink (color bleeding) because the time required for the polyvalent metal salt in the treatment liquid to react as an aggregating agent with the coloring material (pigment) in the white ink was insufficient.

For example, aspects of the present invention are as follows.
<1> A treatment liquid application step of applying a treatment liquid containing a polyvalent metal salt to a printing substrate having a Cobb water absorbency of ²⁰ g/m2 or more and 75 g/ ^m2 or less after a contact time with water of 120 seconds, as specified in JIS-P8140;
a white ink applying step of applying a white ink containing a white coloring material and water to form a white ink layer;
a non-white ink applying step of applying a non-white ink containing a non-white colorant and water onto the white ink layer after a time period of 0.5 seconds or more has elapsed without providing a drying step of drying the white ink by a drying means;
A printing method comprising the steps of:
<2> The printing method according to <1>, wherein the step of leaving the printing material for 0.5 seconds or more without providing a drying step of drying the printing material by the drying means is a step of leaving the printing material for 0.5 seconds or more at 15° C. or more and 40° C. or less.
<3> The printing method according to any one of <1> to <2>, wherein the step of leaving the printing material for 0.5 seconds or more is a step of leaving the printing material for 1 second or more and 4 seconds or less at 15° C. or more and 40° C. or less, without providing a drying step of drying the printing material by the drying means.
<4> The printing method according to any one of <1> to <3>, wherein the substrate is a cardboard base paper.
<5> The printing method according to any one of <1> to <4>, wherein the lightness L ^* value of the printed material is 60 or less.
<6> The printing method according to any one of <1> to <5>, wherein after the treatment liquid is applied, the white ink is applied onto the treatment liquid layer without providing a drying step of drying the treatment liquid by a drying unit.
<7> The printing method according to any one of <1> to <6>, wherein the content of the polyvalent metal salt is 7 mass % or more.
<8> The printing method according to any one of <1> to <7>, wherein after the white ink is applied, the non-white ink is applied onto the white ink layer after a time period of 2 seconds to 5 seconds, without drying the white ink layer.
<9> The printing method according to any one of <1> to <8>, wherein in the white ink applying step, the white ink is applied two or more times.
<10> The printing method according to any one of <1> to <9>, further comprising a drying step of drying the printing substrate to which the non-white ink has been applied.
<11> The printing method according to any one of <1> to <10>, wherein in the white ink applying step and the non-white ink applying step, the white ink and the non-white ink are applied by an inkjet system.
<12> A treatment liquid applying means for applying a treatment liquid containing a polyvalent metal salt to a printing substrate having a Cobb water absorbency of 20 g/m2 or ^more and 75 g/ ^m2 or less when contacted with water for 120 seconds, as specified in JIS-P8140;
a white ink applying means for applying a white ink containing a white color material and water to form a white ink layer;
a non-white ink applying means for applying a non-white ink containing a non-white coloring material and water onto the white ink layer after a time period of 0.5 seconds or more has elapsed without providing a drying step of drying the white ink by a drying means;
The printing device is characterized by having:
<13> The printing device according to <12>, further comprising a drying unit that dries the printing medium to which the non-white ink has been applied.
<14> On a substrate having a Cobb water absorption of 20 g/m2 ^{or more} and 75 g/m2 or ^less at a contact time of 120 seconds with water as specified in JIS-P8140,
a treatment liquid layer containing a polyvalent metal salt;
a white ink layer containing a white colorant;
a non-white ink layer containing a non-white colorant;
The printed matter is characterized by having the following:

The printing method described in any one of <1> to <11>, the printing device described in any one of <12> to <13>, and the printed matter described in <14> can solve the problems of the past and achieve the object of the present invention.

REFERENCE SIGNS LIST 1 Printing substrate 2 Treatment liquid application device 3 White ink ejection head 4 Non-white ink (color ink) ejection head 5 First drying device 6 Second drying device 7 Conveyor belt 100 Printing device

Patent No. 6140908 JP 2014-83789 A

Claims (13)

a treatment liquid application step of applying a treatment liquid containing a polyvalent metal salt to a printing substrate having a Cobb water absorbency of 20 g/m2 or ^more and 75 g/m2 or ^less at a contact time with water of 120 seconds as specified in JIS-P8140;
a white ink applying step of applying a white ink containing a white coloring material and water to form a white ink layer;
a non-white ink applying step of applying a non-white ink containing a non-white colorant and water onto the white ink layer after a time period of 0.5 seconds or more has elapsed without providing a drying step of drying the white ink by a drying means;
A printing method comprising: The printing method according to claim 1, wherein the step of leaving the printing material for 0.5 seconds or more without providing a drying step in which the printing material is dried by the drying means is a step of leaving the printing material for 0.5 seconds or more at a temperature of 15°C or more and 40°C or less. The printing method according to any one of claims 1 to 2, in which the step of leaving the printing material for 0.5 seconds or more without providing a drying step in which the printing material is dried by the drying means is a step of leaving the printing material for 1 second or more and 4 seconds or less at 15°C or more and 40°C or less. The printing method according to any one of claims 1 to 3, wherein the substrate is a cardboard base paper. The printing method according to claim 1 , wherein the lightness L ^* value of the printed material is 60 or less. The printing method according to claim 1 , wherein after the treatment liquid is applied, the white ink is applied onto the treatment liquid layer without providing a drying step in which the treatment liquid is dried by a drying means. The printing method according to any one of claims 1 to 6, wherein the content of the polyvalent metal salt is 7% by mass or more. The printing method according to any one of claims 1 to 7, wherein after applying the white ink, the non-white ink is applied onto the white ink layer without drying the white ink layer after a time period of 2 to 5 seconds. The printing method according to any one of claims 1 to 8, wherein the white ink is applied two or more times in the white ink application process. The printing method according to any one of claims 1 to 9, further comprising a drying step of drying the printed material to which the non-white ink has been applied. The printing method according to any one of claims 1 to 10, wherein in the white ink application process and the non-white ink application process, the white ink and the non-white ink are applied by an inkjet method. a treatment liquid applying means for applying a treatment liquid containing a polyvalent metal salt to a printing substrate having a Cobb water absorbency of 20 g/ ^m2 or ^more and 75 g/m2 or less when contacted with water for 120 seconds as specified in JIS-P8140;
a white ink applying means for applying a white ink containing a white color material and water to form a white ink layer;
a non-white ink applying means for applying a non-white ink containing a non-white coloring material and water onto the white ink layer after a time period of 0.5 seconds or more has elapsed without providing a drying step of drying the white ink by a drying means;
A printing device comprising: The printing device according to claim 12, further comprising a drying means for drying the printing substrate to which the non-white ink has been applied.