WO2022158339A1 - Ink-jet recording method - Google Patents

Abstract

This ink-jet recording method comprises applying a precoating fluid to a base, printing a water-based ink simultaneously therewith or immediately thereafter, and drying the water-based ink, wherein the precoating fluid contains an organic acid or a polyvalent-metal salt and the water-based ink comprises a pigment, a dispersion of fine resin particles, water, and an organic solvent, the dispersion of fine resin particles satisfying requirement (I).　Requirement (I): A liquid mixture prepared by adding an aqueous malonic acid solution to the dispersion of fine resin particles so as to result in a content of the fine resin particles of 5 mass% and a malonic acid concentration of 10 mmol/L has a pH at 25°C of 5 or lower.

Description

Inkjet recording method

The present invention relates to an inkjet recording method, and more particularly to an inkjet recording method capable of improving image quality and having good adhesion.

Since the inkjet recording method can easily and inexpensively create images, it has been applied to various printing fields including special printing such as photography, various printing, marking, and color filters. In particular, the inkjet recording method enables digital printing without using a plate, and is particularly suitable for applications such as forming various images in small quantities.

In such an inkjet recording method, a pre-coating liquid containing an organic acid or a polyvalent metal salt is applied to the base material in advance, whereby the pigment contained in the ink is aggregated by the organic acid or the polyvalent metal salt, resulting in pinning. A technique for obtaining a high-quality image record is disclosed (see Patent Document 1, for example).
Further, in order to fix the pigment on the base material after printing and drying, it is common to incorporate a fine resin particle dispersion into the ink.
However, depending on the resin fine particle dispersion added to the ink, when an organic acid or polyvalent metal salt is added to the ink, the resin fine particle dispersion may inhibit the aggregation of the pigment. The image quality was greatly deteriorated, such as twisting and low gloss and poor adhesion after drying.

JP 2009-202596 A

The present invention has been made in view of the above problems and circumstances, and the problem to be solved is to provide an inkjet recording method that can improve image quality by aggregating pigments and pinning them at the time of printing, and also has good adhesion. to provide.

In order to solve the above problems, the inventors of the present invention, in the process of studying the causes of the above problems, found that the resin fine particle dispersion contained in the water-based ink had a pH of 5 or less at 25 ° C. by titration with an aqueous malonic acid solution. By using the resin fine particle dispersion before titration, it is possible to prevent the resin fine particles from reacting with the organic acid or polyvalent metal salt in the precoating liquid and inhibiting the decrease in pH or from aggregating during printing. The present inventors have found that it is possible to provide an ink jet recording method with improved image quality and good adhesion, and have completed the present invention.
That is, the above problems related to the present invention are solved by the following means.

1. An inkjet recording method in which a water-based ink is printed and dried at the same time or immediately after applying a precoat liquid to a substrate,
the precoat liquid contains an organic acid or a polyvalent metal salt,
the water-based ink contains a pigment, a fine resin particle dispersion, water, and an organic solvent, and
An inkjet recording method in which the fine resin particle dispersion satisfies the following condition (I).
Condition (I): In a mixed solution prepared by adding an aqueous malonic acid solution to the fine resin particle dispersion so that the fine resin particles are 5% by mass and the malonic acid is 10 mmol/L, the pH at 25° C. is 5 or less.

2. 2. The inkjet recording method according to claim 1, wherein the fine resin particles do not aggregate in the mixed liquid.

3. The resin fine particles contained in the resin fine particle dispersion liquid are acrylic resin fine particles, urethane resin fine particles, or polyester resin fine particles, and
3. The inkjet recording method according to item 1 or item 2, wherein the average particle diameter is 200 nm or less.

4. 4. The inkjet recording method according to any one of items 1 to 3, wherein the pigment is a self-dispersing pigment having an anionic group on its surface.

5. 4. The inkjet recording method according to any one of items 1 to 3, wherein the pigment is dispersed with an anionic polymeric dispersant.

6. 4. The inkjet recording method according to any one of items 1 to 3, wherein the pigment is dispersed with its surface coated with an anionic resin.

7. 7. The inkjet recording method according to any one of items 1 to 6, wherein the inkjet recording method is a single pass system.

8. 8. The inkjet recording method according to any one of items 1 to 7, wherein the precoat liquid is applied to the substrate by an inkjet method.

9. 9. The organic acid according to any one of items 1 to 8, wherein the organic acid has a first dissociation constant pK _a1 within the range of 1.5 to 4 at a temperature of 25°C. Inkjet recording method.

10. Any one of items 1 to 9 containing a polyvalent metal salt selected from calcium chloride, magnesium chloride, calcium nitrate, magnesium nitrate, and calcium salts and magnesium salts of carboxylic acids as the polyvalent metal salt. The ink jet recording method according to the item.

By means of the above means of the present invention, it is possible to provide an ink jet recording method capable of improving image quality by aggregating pigments and causing pinning during printing, and having good adhesion.
Although the expression mechanism or action mechanism of the effect of the present invention has not been clarified, it is speculated as follows.
In general, an alkali component is often added to the fine resin particle dispersion liquid added to the ink for the purpose of neutralizing the acid component and improving the dispersibility of the fine resin particles.
However, it is thought that such an alkali component reacts with the organic acid or polyvalent metal salt in the precoat liquid before the pigment in the ink reacts, thereby delaying the pinning of the pigment and degrading the image quality.
In addition, if the fine resin particles react with the organic acid or polyvalent metal salt in the pre-coating liquid and agglomerate, the film-forming property deteriorates during drying after printing, resulting in a marked decrease in glossiness and poor adhesion. it is conceivable that.

Therefore, it has been found that the fine resin particle dispersion added to the ink is preferably one that does not react with the organic acid or polyvalent metal salt in the precoating liquid to hinder the decrease in pH or cause agglomeration.
In particular, when high-speed pinning is required, such as in single-pass printing, the effect of such resin fine particle dispersions is large, and the organic acids and polyvalent metal salts in the precoat liquid react to cause pigment aggregation. If a fine resin particle dispersion that interferes with the ink is added to the ink, the image quality is remarkably degraded.
Also, in the case of a method in which the precoat liquid is also printed by an inkjet method at the same time as or immediately before the printing of the ink, the precoat liquid is hardly dried and concentrated, and is mixed with the ink to develop the pinning property. Since it is necessary to coagulate the pigment even in a dilute state, it is highly susceptible to reaction with the organic acid and polyvalent metal salt of the fine resin particle dispersion.
As a method for measuring such properties of the resin fine particle dispersion, the resin fine particle dispersion is titrated with an organic acid (malonic acid) added to the precoating liquid, and the pH change and aggregation are observed. It was found that the degree of influence on pinning properties, adhesion, etc. can be estimated.

As described above, in the present invention, the resin fine particle dispersion contained in the water-based ink is obtained by adding a malonic acid aqueous solution to the resin fine particle dispersion so that the resin fine particles are 5% by mass and the malonic acid is 10 mmol/L. By using a resin fine particle dispersion having a pH of 5 or less at 25° C. in the mixed liquid prepared so as to It is possible to provide an inkjet recording method that can prevent a decrease in pH and aggregation by coagulating the pigment, has good pinning property by aggregating the pigment, can improve the image quality, and has excellent adhesion. .

Schematic diagram showing an example of precoat/inkjet recording apparatus preferred for the present invention FIG. 1 is a cross-sectional view showing a schematic configuration of an image recorded matter according to the present invention; Cross-sectional view of packaging material for canned food

The inkjet recording method of the present invention is an inkjet recording method in which a water-based ink is printed and dried at the same time or immediately after applying a precoat liquid to a substrate, wherein the precoat liquid contains an organic acid or a polyvalent metal salt, The water-based ink contains a pigment, a fine resin particle dispersion, water, and an organic solvent, and the fine resin particle dispersion satisfies the following condition (I).
Condition (I): In a mixed solution prepared by adding an aqueous malonic acid solution to the fine resin particle dispersion so that the fine resin particles are 5% by mass and the malonic acid is 10 mmol/L, the pH at 25° C. is 5 or less.
This feature is a technical feature common to or corresponding to each of the following embodiments.

As an embodiment of the present invention, it is preferable that the fine resin particles do not aggregate in the mixture.
Here, "the resin fine particles aggregate" means that when an aqueous solution of malonic acid is added to the resin fine particle dispersion, the dispersion becomes unstable and the fine particles adsorb and aggregate to increase the average particle diameter. refers to the phenomenon of sedimentation. In general dispersions, the particle size of the dispersion is often 1,000 nm or less, but when aggregated, the fine particles are adsorbed and aggregated to each other, resulting in an average particle size of 1,000 nm or more, and in some cases, sedimentation. Therefore, in the present invention, "the fine resin particles do not aggregate" means that no sedimentation occurs in the mixed solution to which the aqueous malonic acid solution is added, and the average particle size is maintained at less than 1000 nm. By using such a resin fine particle dispersion in which the resin fine particles do not aggregate in the water-based ink, the pinning property is improved, and the image quality is improved and the adhesion is excellent, which is preferable.

Further, the resin fine particles contained in the resin fine particle dispersion liquid are acrylic resin fine particles, urethane resin fine particles or polyester resin fine particles, and have an average particle diameter of 200 nm or less. It is preferable in that the coating tends to be uniform, the image quality is not uneven, and the adhesion is excellent.

The pigment is a self-dispersing pigment having an anionic group on the surface, is dispersed with an anionic polymer dispersant, or is dispersed with the surface coated with an anionic resin. , is preferable in terms of excellent dispersibility.

The inkjet recording method is preferably a single-pass method in terms of effectively exhibiting the effects of the present invention.

It is preferable to apply the precoat liquid to the base material by an ink jet method because it is simple and inexpensive, and can be applied with high accuracy.

As the organic acid, the first dissociation constant pK _a1 of the acid is contained in the range of 1.5 to 4 at a temperature of 25 ° C. Further preventing the liquid from sticking in the low density area where the printing rate is low This is preferable in that beading can be further improved in high-density areas where the printing rate is high.
In addition, as the polyvalent metal salt, it is preferable to contain a polyvalent metal salt selected from calcium chloride, magnesium chloride, calcium nitrate, magnesium nitrate, and calcium salt or magnesium salt of carboxylic acid. is high and the pigment in the water-based ink can be reliably aggregated.

The following describes the present invention, its constituent elements, and the forms and modes for carrying out the present invention. In the present application, "-" is used to mean that the numerical values before and after it are included as the lower limit and the upper limit.

[Overview of the inkjet recording method of the present invention]
The inkjet recording method of the present invention (hereinafter also simply referred to as "inkjet method") is an inkjet recording method in which a water-based ink is printed and dried at the same time or immediately after applying a precoat liquid to a substrate, and the precoat liquid is contains an organic acid or a polyvalent metal salt, the water-based ink contains a pigment, a resin fine particle dispersion, water, and an organic solvent, and the resin fine particle dispersion satisfies the following condition (I): Fulfill.
Condition (I): In a mixed solution prepared by adding an aqueous malonic acid solution to the fine resin particle dispersion so that the fine resin particles are 5% by mass and the malonic acid is 10 mmol/L, the pH at 25° C. is 5 or less.
More preferably, the pH is in the range of 2-4.

That is, the fine resin particle dispersion contained in the water-based ink according to the present invention is titrated with an organic acid contained in the precoat liquid, specifically, an aqueous solution of malonic acid, and is such that the pH at 25° C. is 5 or less. By using the resin fine particle dispersion liquid before titration, it is possible to prevent the resin fine particles from reacting with the organic acid or polyvalent metal salt in the precoat liquid and preventing the decrease in pH or agglomeration at the time of printing.
Specifically, for example, an aqueous solution of malonic acid is added to a commercially available fine resin particle dispersion to prepare a mixed liquid so that the resin fine particles are 5% by mass and the malonic acid is 10 mmol/L. Then, when the prepared mixed liquid exhibits a pH of 5 or less at 25° C., the commercially available resin fine particle dispersion of the mixed liquid showing such a pH of 5 or less before the addition of the aqueous malonic acid solution is used. is preferably used to prepare an aqueous ink.

Further, it is preferable that the resin fine particles do not aggregate in the mixed liquid. Further, the average particle diameter of the fine resin particles in the mixed liquid is preferably within the range of 100 to 500 nm, in order to prevent aggregation of the fine resin particles in the mixed liquid.

In the inkjet recording method of the present invention, the water-based ink may be applied continuously without drying after applying the pre-coating liquid, in which case the pre-coating liquid is dried together with the water-based ink.

The inkjet recording method of the present invention is not particularly limited in its application. A high-quality image can be recorded on a non-absorbent base material by recording an ink image using .

"Precoating liquid" and "aqueous ink" as used in the present invention refer to "precoating liquid" and "ink" that use at least "water" as a solvent. In all cases, 60% by mass or more of the solvent used is "water".

[1] Substrate The substrate that can be used in the present invention is not particularly limited, but is preferably a non-absorbent substrate. In the present invention, "non-absorbent" refers to non-absorbent to water.

A known plastic film can be used as an example of the non-absorbent substrate. Specific examples include polyester films such as polyethylene terephthalate, polyethylene films, polypropylene films, polyamide films such as nylon, polystyrene films, polyvinyl chloride films, polycarbonate films, polyacrylonitrile films, biodegradable films such as polylactic acid films, and the like. is mentioned.
In addition, in order to impart gas barrier properties, moisture resistance, fragrance retention properties, etc., a film coated with polyvinylidene chloride on one or both sides thereof, or a film deposited with a metal oxide can also be preferably used. The non-water-absorbent film can be preferably used whether it is an unstretched film or a stretched film.
The thickness of the substrate is preferably in the range of 10-120 μm, more preferably 12-60 μm in the case of a plastic film.

As non-absorbent substrates, metal substrates such as tin plates for three-piece cans and tin-free steel plates (TFS plates, thickness 0.1 to 0.6 μm) are also preferably used. It can be suitably used as a packaging material for canned foods, which is provided with a resin as a coating layer. The packaging material for canned food, for example, blocks air, moisture, and light, and seals the food inside.
Polyester-based and acrylic-based thermosetting paints are generally used for the outside.

[2] Precoat liquid The precoat liquid according to the present invention accelerates ink image formation, improves physical properties of the precoat layer and ink layer, and improves image quality when recording an image on a substrate by an inkjet printing method. can have the ability to improve
Specifically, in the present invention, by printing the ink according to the present invention on the substrate at the same time or immediately after applying the precoat liquid according to the present invention, even if the substrate is non-absorbent, It is possible to perform recording excellent in image quality, water resistance and hot water resistance, and excellent adhesion between the non-absorbent base material and the precoat layer.

The precoat liquid according to the present invention contains an organic acid or polyvalent metal salt. Moreover, it is preferable to contain water as a solvent.

(coagulant)
The precoating liquid according to the present invention contains a material that forms an aggregate when it comes into contact with an aqueous ink containing a pigment, that is, an organic acid or a polyvalent metal salt, which is a flocculant. The greater the interaction, the more the water-based ink dots can be fixed.

The flocculant preferably contains either an organic acid or a polyvalent metal salt, more preferably an organic acid.

The polyvalent metal salt can aggregate anionic components (usually coloring materials, pigments, etc.) in the water-based ink by salting out. The organic acid can aggregate the anionic component in the water-based ink by pH fluctuation.

As the polyvalent metal salt, a salt of a metal having a valence of 2 or more can be used. The type of ^metal ( ^cation ) that ^constitutes the ^{polyvalent metal salt} is not ^{particularly limited} . , Cr ³⁺ , Y ³⁺ and other trivalent metal ions, and Zr ⁴⁺ and other tetravalent metal ions.
The type of salt that constitutes the polyvalent metal salt is not particularly limited, but known salts such as carbonates, sulfates, nitrates, hydrochlorides, organic acid salts, borates, and phosphates can be used. Specific examples of particularly preferred polyvalent metal salts include calcium salts and magnesium salts of carboxylic acids such as calcium chloride, magnesium chloride, calcium nitrate, magnesium nitrate, calcium acetate and magnesium lactate.

The organic acid is capable of aggregating pigments that may be contained in aqueous inks.
Examples of the organic acid include formic acid, acetic acid, propionic acid, isobutyric acid, oxalic acid, fumaric acid, malic acid, citric acid, malonic acid, succinic acid, maleic acid, benzoic acid, and 2-pyrrolidone-5-carboxylic acid. , lactic acid, acrylic acid or its derivatives, methacrylic acid or its derivatives, acrylamide or its derivatives, sulfonic acid derivatives and the like.
Particularly preferred organic acids preferably have a first dissociation constant pK _a1 within the range of 1.5-4. This further prevents the liquid from dripping in the low-density area where the printing rate is low, and further improves the beading in the high-density area where the printing rate is high.
Specific organic acids having a pK _a1 of 1.5 to 4 include formic acid, oxalic acid, fumaric acid, malic acid, citric acid, malonic acid, maleic acid, 2-pyrrolidone-5-carboxylic acid, and the like. be done.

It is preferable to use an organic acid that has not been completely neutralized with a base. Neutralization with a base means that the acidic groups of these acids are ionically bonded with other positively charged elements or compounds (eg, inorganic compounds such as metals). In addition, "not completely neutralized" means that among the acidic groups of the organic acid, there are acidic groups that do not form the above ionic bond.
In addition, by using an organic acid, it is easy to maintain the storage stability of the precoating liquid, and blocking hardly occurs after the precoating liquid is applied and dried. Preferred organic acids from the above viewpoint are formic acid, acetic acid, propionic acid, isobutyric acid, oxalic acid, fumaric acid, malic acid, citric acid, malonic acid, succinic acid, maleic acid, benzoic acid, and 2-pyrrolidone-5-carboxylic acid. , lactic acid, acrylic acid and its derivatives, methacrylic acid and its derivatives, or acrylamide and its derivatives, compounds having a carboxy group, sulfonic acid derivatives, or phosphoric acid and its derivatives.

The content of the organic acid in the precoating liquid may be any amount that adjusts the pH of the precoating liquid to be less than the first dissociation constant of the organic acid. Bleeding during high-speed printing can be effectively suppressed by including an amount of the organic acid in the precoating liquid that makes the pH of the precoating liquid less than the first dissociation constant of the organic acid.

Examples of the polyvalent metal salts include water-soluble salts such as calcium salts, magnesium salts, aluminum salts and zinc salts.

The organic acid or the polyvalent metal salt is preferably contained in a range of 5% by mass or less, preferably in a range of 0.1 to 3% by mass, with respect to the precoat liquid, and further, 0 The content within the range of 0.5 to 1.0% by mass is preferable from the viewpoint of effectively aggregating the anionic component in the water-based ink and balancing image quality and hot water resistance.

The content of the organic acid or polyvalent metal salt in the aqueous solution can be measured by a known method. For example, the content can be measured by ICP emission spectrometry in the case of polyvalent metal salts, and by high performance liquid chromatography (HPLC) in the case of organic acids.

When an organic acid is used, the amount of organic acid added is preferably an amount that adjusts the pH of the precoat liquid to a neutralization equivalent or less of the anionic component contained in the water-based ink. Further, when the anion component is a compound having a carboxyl group, the first dissociation constant of the organic acid is preferably 3.5 or less from the viewpoint of making image bleeding less likely to occur.

The application amount of the precoating liquid of the present invention is not particularly limited, and can be adjusted as appropriate. For example, when a polyvalent metal salt is used, the amount of the polyvalent metal salt to be applied is preferably in the range of 0.1 to 20 g/m ² . In the case of an organic acid, the amount of the organic acid to be added is preferably equal to or less than the neutralization equivalent of the anion component in the water-soluble ink.

(water, other additives)
The water contained in the precoat liquid according to the present invention is not particularly limited, and may be ion-exchanged water, distilled water, or pure water.

In addition to water, an organic solvent can be contained as a solvent for the precoating liquid according to the present invention. The solvent can be removed during the subsequent drying of the precoating liquid.

The pre-coating liquid can appropriately contain other components such as surfactants, cross-linking agents, antifungal agents, and bactericides within the range that does not impair the effects of the present invention.

Furthermore, for example, the UV absorber described in JP-A-57-74193, JP-A-57-87988 and JP-A-62-261476, JP-A-57-74192, JP-A-57-87989, JP-A-60 -72785, JP-A-61-146591, JP-A-1-95091 and JP-A-3-13376 anti-fading agents, various anionic, cationic or nonionic surfactants, JP-A-59 No. -42993, No. 59-52689, No. 62-280069, No. 61-242871 and JP-A-4-219266, fluorescent whitening agents, defoaming agents, lubricants such as diethylene glycol Various known additives such as agents, preservatives, thickeners, antistatic agents, etc. can also be contained.

It is preferable to prepare the precoat layer by applying the precoat liquid according to the present invention as a coating liquid directly onto the substrate and drying it. Here, it is preferable that the additive preferably used in the precoating liquid is sufficiently dissolved before being used as the coating liquid.

As a method for applying the precoat liquid, an ink jet method, a roll coating method, a rod bar coating method, an air knife coating method, a spray coating method, a curtain coating method, or an extrusion coating method using a hopper described in US Pat. No. 2,681,294 is preferably used. , especially the inkjet method is preferred.

[3] Aqueous Ink The aqueous ink (hereinafter also referred to as "ink liquid" or simply "ink") according to the present invention contains at least a pigment, a fine resin particle dispersion, water and an organic solvent. Furthermore, it is preferable to contain a pigment dispersion liquid for dispersing the pigment.
Further, as described above, the fine resin particle dispersion used in the water-based ink according to the present invention satisfies the condition (I) described above.

(pigment)
Pigments contained in the ink according to the present invention include anionic dispersed pigments, for example, self-dispersing pigments having an anionic group on the surface, pigments dispersed by an anionic polymer dispersant, and anionic pigments on the surface. It is preferable to use a pigment coated and dispersed with a flexible resin.

As the pigment, conventionally known pigments can be used without particular limitation. For example, organic pigments such as insoluble pigments and lake pigments, and inorganic pigments such as titanium oxide can be preferably used.

In titanium oxide, for which it is generally difficult to ensure ink ejection stability and adhesion, the present invention makes it possible to prevent bleeding and improve adhesion, particularly preferably.

　Titanium oxide has three crystal forms: anatase, rutile, and brookite. General-purpose forms can be roughly divided into anatase and rutile. Although not particularly limited, the rutile type having a high refractive index and high hiding power is preferable. Specific examples include the TR series of Fuji Titanium Industry Co., Ltd., the JR series of Tayca Co., Ltd., and the Typaque of Ishihara Sangyo Co., Ltd.

Examples of insoluble pigments include, but are not limited to, azo, azomethine, methine, diphenylmethane, triphenylmethane, quinacridone, anthraquinone, perylene, indigo, quinophthalone, isoindolinone, isoindoline, azine, oxazine, thiazine, Dioxazines, thiazoles, phthalocyanines, diketopyrrolopyrroles and the like are preferred.

Specific organic pigments that can be preferably used include the following pigments.

As pigments for magenta or red, for example, C.I. I. Pigment Red 2, C.I. I. Pigment Red 3, C.I. I. Pigment Red 5, C.I. I. Pigment Red 6, C.I. I. Pigment Red 7, C.I. I. Pigment Red 15, C.I. I. Pigment Red 16, C.I. I. Pigment Red 48:1, C.I. I. Pigment Red 53:1, C.I. I. Pigment Red 57:1, C.I. I. Pigment Red 122, C.I. I. Pigment Red 123, C.I. I. Pigment Red 139, C.I. I. Pigment Red 144, C.I. I. Pigment Red 149, C.I. I. Pigment Red 166, C.I. I. Pigment Red 177, C.I. I. Pigment Red 178, C.I. I. Pigment Red 202, C.I. I. Pigment Red 222, C.I. I. Pigment Violet 19 and the like.

As pigments for orange or yellow, for example, C.I. I. Pigment Orange 31, C.I. I. Pigment Orange 43, C.I. I. Pigment Yellow 12, C.I. I. Pigment Yellow 13, C.I. I. Pigment Yellow 14, C.I. I. Pigment Yellow 15, C.I. I. Pigment Yellow 15:3, C.I. I. Pigment Yellow 17, C.I. I. Pigment Yellow 74, C.I. I. Pigment Yellow 93, C.I. I. Pigment Yellow 128, C.I. I. Pigment Yellow 94, C.I. I. Pigment Yellow 138, C.I. I. Pigment Yellow 155 and the like. Especially in the balance between color tone and light resistance, C.I. I. Pigment Yellow 155 is preferred.

As pigments for green or cyan, for example, C.I. I. Pigment Blue 15, C.I. I. Pigment Blue 15:2, C.I. I. Pigment Blue 15:3, C.I. I. Pigment Blue 16, C.I. I. Pigment Blue 60, C.I. I. Pigment Green 7 and the like.

Also, as black pigments, for example, C.I. I. Pigment Black 1, C.I. I. Pigment Black 6, C.I. I. Pigment Black 7 and the like.

(Pigment dispersant)
The pigment dispersant used to disperse the pigment is not particularly limited, but a polymeric dispersant having an anionic group is preferred, and those having a molecular weight within the range of 5,000 to 200,000 can be suitably used.

Examples of polymer dispersants include 2 selected from styrene, styrene derivatives, vinylnaphthalene derivatives, acrylic acid, acrylic acid derivatives, maleic acid, maleic acid derivatives, itaconic acid, itaconic acid derivatives, fumaric acid, and fumaric acid derivatives. Block copolymers, random copolymers and salts thereof, polyoxyalkylenes, polyoxyalkylene alkyl ethers, etc. having structures derived from more than one kind of monomers can be mentioned.

The polymer dispersant preferably has an acryloyl group and is preferably added after being neutralized with a neutralizing base. Although the neutralizing base is not particularly limited here, it is preferably an organic base such as ammonia, monoethanolamine, diethanolamine, triethanolamine or morpholine. In particular, when the pigment is titanium oxide, the titanium oxide is preferably dispersed with a polymer dispersant having an acryloyl group.

The amount of polymer dispersant added is preferably in the range of 10 to 100% by mass, more preferably in the range of 10 to 40% by mass, based on the pigment.

The pigment is particularly preferably in the form of a so-called capsule pigment, in which the pigment is coated with the polymer dispersant. As a method for coating the pigment with the polymer dispersant, various known methods can be used. For example, the phase inversion emulsification method, the acid precipitation method, or the A preferred example is a method of supplying a monomer to the film and coating the film while polymerizing the film.

As a particularly preferred method, a water-insoluble resin is dissolved in an organic solvent such as methyl ethyl ketone, and after partially or completely neutralizing the acidic groups in the resin with a base, a pigment and ion-exchanged water are added and dispersed. After that, the organic solvent is removed, and if necessary, water is added for preparation.

The average particle diameter of the dispersed pigment in the ink is preferably 50 nm or more and less than 200 nm. Thereby, the dispersion stability of the pigment can be improved, and the storage stability of the ink can be improved. The particle size of the pigment can be determined by a commercially available particle size measuring instrument using a dynamic light scattering method, an electrophoresis method, or the like. Accurate measurement is possible.

The pigment can be used by dispersing it with a dispersing machine together with a dispersant and other additives necessary for various desired purposes.

As a disperser, conventionally known ball mills, sand mills, line mills, high pressure homogenizers, etc. can be used. Among them, it is preferable to disperse the pigment by a sand mill because the particle size distribution becomes sharp. The material of the beads used for sand mill dispersion is not particularly limited, but zirconia or zircon is preferable from the viewpoint of preventing the generation of bead fragments and contamination with ionic components. Furthermore, the bead diameter is preferably within the range of 0.3 to 3 mm.

Although the content of the pigment in the ink is not particularly limited, it is preferably in the range of 7 to 18% by mass for titanium oxide, and 0.5 to 7% by mass for the organic pigment.

(resin fine particle dispersion)
The fine resin particle dispersion of the water-based ink according to the present invention is preferably a dispersion of water-insoluble fine resin particles. The water-insoluble resin fine particles used in the present invention are fine particle dispersions of a water-insoluble resin that can accept ink and exhibit solubility or affinity for the ink.

The water-insoluble resin fine particles are originally water-insoluble, but have a form in which the resin is dispersed in an aqueous medium as microfine particles. or a non-water-soluble resin capable of self-emulsification that forms a stable aqueous dispersion by itself without using an emulsifier or dispersion stabilizer by introducing a hydrophilic functional group into the molecule. These resins are usually used in a state of being emulsified and dispersed in water or a water/alcohol mixed solvent.

In the present invention, the term “water-insoluble” means that when the resin is dried at 105° C. for 2 hours and then dissolved in 100 g of water at 25° C., the dissolved amount is 10 g or less, preferably 5 g or less, and further Preferably, it refers to a resin weighing 1 g or less. However, when the resin has a salt-forming group, the dissolved amount is the dissolved amount when the salt-forming group of the resin is 100% neutralized with acetic acid or sodium hydroxide, depending on the type.

The resin fine particle dispersion satisfies the condition (I) as described above. That is, in a mixed liquid prepared by adding a malonic acid aqueous solution to a resin fine particle dispersion liquid so that the resin fine particles are 5% by mass and the malonic acid is 10 mmol/L, the pH at 25° C. is 5 or less. . Then, by using the fine resin particle dispersion having a pH of 5 or less, the fine resin particles in the water-based ink are prepared to have a predetermined concentration.

As for the predetermined concentration, the fine resin particles in the ink are preferably in the range of 3 to 10 mass %.
The resin fine particles in the resin fine particle dispersion are preferably acrylic resin fine particles, urethane resin fine particles, polyester resin fine particles, or composite resin fine particles of urethane resin and acrylic resin, and particularly acrylic resin fine particles and urethane resin fine particles. , polyester resin fine particles or composite resin fine particles of urethane resin and acrylic resin, and the average particle diameter of the resin fine particles is preferably 200 nm or less. In particular, the average particle size is preferably within the range of 100-150 nm.

The polyester resin, urethane resin, acrylic resin, or composite resin particles of urethane resin and acrylic resin are preferably anionic or nonionic.

Among them, the fine resin particles used in water-based inks preferably contain an acid structure, and even if the amount of surfactant added is small, they can be dispersed in water and the water resistance of the ink layer is improved. This is called a self-emulsifying type, which means that the urethane-based resin can be dispersed and stabilized in water only with molecular ionic properties without using a surfactant. Examples of acid structures include acid groups such as a carboxy group (--COOH) and a sulfonic acid group (--SO ₃ H). The acid structure may be present in the side chain of the resin, or may be present at the end.

A part or all of the acid structure is preferably neutralized. By neutralizing the acid structure, the water dispersibility of the resin can be improved. Examples of neutralizing agents that neutralize the acid structure are preferably organic amines, and organic amines such as trimethylamine, triethylamine, tripropylamine, tributylamine, N-methyldiethanolamine and triethanolamine are preferably used.

Further, the glass transition point (Tg) of the fine resin particles according to the present invention is preferably within the range of 0 to 100.degree.
The glass transition point (Tg) is determined from the endothermic peak when the temperature is raised in the temperature range of −30 to 200° C. at a temperature elevation rate of 10° C./min using a DSC (differential scanning calorimeter). It can be identified by reading the transition temperature Tg.

Each resin will be described below.
(polyester resin)
A polyester resin having a polyester skeleton as water-insoluble resin fine particles can be obtained by using a polyhydric alcohol component and a polycarboxylic acid component such as a polycarboxylic acid, a polycarboxylic anhydride, or a polycarboxylic acid ester. can.

As the polyhydric alcohol component, a dihydric alcohol (diol), specifically an alkylene glycol having 2 to 36 carbon atoms (ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1 , 4-butylene glycol, 1,6-hexanediol, etc.), alkylene ether glycols having 4 to 36 carbon atoms (diethylene glycol, triethylene glycol, dipropylene glycol, polyethylene glycol, polypropylene glycol, polybutylene glycol, etc.), Alicyclic diols having 6 to 36 carbon atoms (1,4-cyclohexanedimethanol, hydrogenated bisphenol A, etc.), alkylene oxides having 2 to 4 carbon atoms (ethylene oxide (hereinafter referred to as , abbreviated as EO.), propylene oxide (hereinafter abbreviated as PO.), butylene oxide (hereinafter abbreviated as BO.)) adduct (addition mole number range of 1 to 30) or bisphenols (bisphenol A , bisphenol F, bisphenol S, etc.) with 2 to 4 carbon atoms (EO, PO, BO, etc.) adducts (addition mole number in the range of 2 to 30), and the like. These may be used individually by 1 type, and may use 2 or more types together.

Examples of the polyvalent carboxylic acid component include divalent carboxylic acids (dicarboxylic acids), specifically alkanedicarboxylic acids having 4 to 36 carbon atoms (succinic acid, apidic acid, sebacic acid, etc.), alkenylsuccinic acids. (dodecenyl succinic acid, etc.), alicyclic dicarboxylic acids having 4 to 36 carbon atoms (dimer acid (dimerized linoleic acid), etc.), alkenedicarboxylic acids having 4 to 36 carbon atoms (maleic acid, fumaric acid , citraconic acid, mesaconic acid, etc.), or aromatic dicarboxylic acids having 8 to 36 carbon atoms (phthalic acid, isophthalic acid, terephthalic acid or derivatives thereof, naphthalenedicarboxylic acid, etc.). These may be used individually by 1 type, and may use 2 or more types together.

The number average molecular weight of the polyester resin is preferably in the range of 1,000 to 50,000, more preferably in the range of 2,000 to 20,000.

As the polyester resin, a commercially available product may be used. Examples of the commercially available products include Pesresin A-110F, A-640, A-647GEX manufactured by Takamatsu Yushi Co., Ltd., Vylonal MD-1100 manufactured by Toyobo Co., Ltd., MD- 1200, MD-1335, MD-1480, MD-1930, MD-2000, Z-1100 manufactured by Goo Chemical Co., Ltd., and the like. These may be used individually by 1 type, and may use 2 or more types together.

(urethane resin)
A urethane resin having a hydrophilic group can be used as the water-insoluble resin fine particles.

The above urethane resin is an aqueous dispersion in which a self-emulsifying urethane having a water-soluble functional group in its molecule is dispersed, or a forced emulsifying urethane emulsified under strong mechanical shearing force in combination with a surfactant. An aqueous dispersion is preferred. The urethane resin in the aqueous dispersion can be obtained by reacting a polyol with an organic polyisocyanate and a hydrophilic group-containing compound.

Examples of polyols that can be used for preparing the aqueous dispersion of the urethane resin include polyester polyols, polyether polyols, polycarbonate polyols, and polyolefin polyols.

Examples of polyester polyols include ethylene glycol, diethylene glycol, triethylene glycol, 1,2- and 1,3-propylene glycol, neopentyl glycol, 1,3- and 1,4-butanediol, 3-methylpentanediol, Low-molecular-weight polyols such as hexamethylene glycol, 1,8-octanediol, 2-methyl-1,3-propanediol, bisphenol A, hydrogenated bisphenol A, trimethylolpropane, cyclohexanedimethanol; succinic acid, glutaric acid, adipine Acids, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid, tetrahydrofuranic acid, endomethinetetrahydrofuranic acid, and condensates with polycarboxylic acids such as hexahydrophthalic acid.

Examples of polyether polyols include polyethylene glycol, polypropylene glycol, polyethylene polytetramethylene glycol, polypropylene polytetramethylene glycol, and polytetramethylene glycol.

Examples of polycarbonate polyols can be obtained by reacting carbonic acid derivatives such as diphenyl carbonate, dimethyl carbonate or phosgene with diols. Examples of such diols include ethylene glycol, diethylene glycol, triethylene glycol, 1,2- and 1,3-propylene glycol, neopentyl glycol, 1,3- and 1,4-butanediol, 3-methylpentanediol, hexamethylene glycol, 1,8-octanediol, 2-methyl-1,3-propanediol, bisphenol A, hydrogenated bisphenol A, trimethylolpropane, cyclohexanedimethanol, and the like.

Examples of organic polyisocyanates that can be used for preparing aqueous dispersions of urethane resins include tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), polymeric MDI, xylylene diisocyanate (XDI), tetramethylxylylene diisocyanate. aromatic isocyanates such as (TMXDI); aliphatic isocyanates such as hexamethylene diisocyanate (HMDI); be These may be used individually by 1 type, and may use 2 or more types together.

Examples of hydrophilic group-containing compounds that can be used in the preparation of aqueous dispersions of urethane resins include 2,2-dimethylolpropionic acid, 2,2-dimethylolbutanoic acid, 2,2-dimethylolbutyric acid, 2,2-dimethylolbutyric acid, Carboxylic acid-containing compounds such as 2-dimethylolvaleric acid, glycine, and derivatives thereof such as sodium salts, potassium salts, amine salts; and derivatives thereof such as sodium salts, potassium salts and amine salts.

A urethane resin can be obtained by a known method. For example, a urethane prepolymer can be obtained by mixing the above-described polyol, organic polyisocyanate, and hydrophilic group-containing compound and reacting them at 30 to 130° C. for 30 minutes to 50 hours.

The above urethane prepolymer becomes a urethane resin having a hydrophilic group by extending it with a chain extender and polymerizing it. The chain extender is preferably water and/or an amine compound. By using water or an amine compound as a chain extender, the isocyanate-terminated prepolymer can be efficiently extended by reacting with free isocyanate in a short period of time.

Examples of amine compounds as chain extenders include aliphatic polyamines such as ethylenediamine and triethylenediamine; aromatic polyamines such as metaxylenediamine and toluylenediamine; and polyhydrazino compounds such as hydrazine and adipic acid dihydrazide. The amine compound may contain, together with the polyamine, a monovalent amine such as dibutylamine, methyl ethyl ketoxime, or the like as a reaction terminator, to the extent that polymerization is not greatly hindered.

In synthesizing the urethane prepolymer, a solvent that is inert with isocyanate and capable of dissolving the urethane prepolymer may be used. Examples of these solvents include dioxane, methyl ethyl ketone, dimethylformamide, tetrahydrofuran, N-methyl-2-pyrrolidone, toluene, propylene glycol monomethyl ether acetate, and the like. These hydrophilic organic solvents used in the reaction step are preferably finally removed.

In the synthesis of urethane prepolymers, amine catalysts (e.g., triethylamine, N-ethylmorpholine, triethyldiamine, etc.), tin-based catalysts (e.g., dibutyltin dilaurate, dioctyltin dilaurate, octyl acid) are used to promote the reaction. tin, etc.), and titanium-based catalysts (eg, tetrabutyl titanate, etc.) may be added.

The number average molecular weight of the urethane resin is preferably increased as much as possible by introducing a branched structure or an internal crosslinked structure, and is preferably from 50,000 to 1,000,000. By setting the molecular weight within the above range, the urethane resin becomes difficult to dissolve in a solvent, so that a coating film having excellent weather resistance and water resistance can be obtained. The number average molecular weight (Mn) is a value measured by gel permeation chromatography (GPC). Solvent: tetrahydrofuran (THF), column temperature: 40° C.) can be determined from a calibration curve prepared from polystyrene standard samples.

In addition, a commercially available product may be used as the urethane resin. Examples of commercially available urethane resins include WBR-016U (manufactured by Taisei Fine Chemicals Co., Ltd.), Superflex 620, Superflex 650, Superflex 500M, and Superflex E-2000 (all manufactured by Daiichi Kogyo Seiyaku Co., Ltd., "Super Flex" is a registered trademark of the same company), Permaline UC-20 (manufactured by Sanyo Chemical Industries, Ltd.; "Permaline" is a registered trademark of the same company), and Parasurf UP-22 (manufactured by Ohara Palladium Chemical Co., Ltd.).

(acrylic resin)
The acrylic resin as the water-insoluble resin fine particles can be obtained by using an acrylic acid ester component, a methacrylic acid ester component, or a copolymer with a styrene component or the like.
Examples of acrylic acid ester components and methacrylic acid ester components include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, blue (meth) acrylate, (meth) acrylic acid-2- Hydroxyethyl, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, cyclohexyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, isobornyl (meth)acrylate, (meth)acrylate ) benzyl acrylate, 2-hydroxybutyl (meth)acrylate, benzyl (meth)acrylate, glycidyl (meth)acrylate, (meth)acrylic acid, (di)ethylene glycol di(meth)acrylate, di ( 1,4-butanediol meth)acrylate, 1,6-hexanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, glyceryl di(meth)acrylate, (meth)acrylic Acid-2-ethylhexyl, lauryl (meth)acrylate, stearyl (meth)acrylate, acrylamide and the like are included.

Examples of styrene components include styrene, 4-methylstyrene, 4-hydroxystyrene, 4-acetoxystyrene, 4-acetylstyrene and styrenesulfonic acid. These components may be used alone or in combination of two or more.

The number average molecular weight (Mn) of the acrylic resin is preferably 1,000 to 50,000, more preferably 2,000 to 20,000. When the number average molecular weight (Mn) of the acrylic resin is 1000 or more, the cohesive force of the coating film becomes strong and adhesion is improved. This is because the reduction in particle size is promoted. The number average molecular weight (Mw) is a value measured by gel permeation chromatography (GPC). Solvent: tetrahydrofuran (THF), column temperature: 40° C.) can be determined from a calibration curve prepared from polystyrene standard samples.

Also, as the acrylic resin, a commercially available product may be used. Examples of commercially available acrylic resins include RKW-620, UW-319SX, UW-600, UW-550CS manufactured by Taisei Fine Chemical Co., Ltd., and acrylic resins such as 2682, 2680, 2684, 2685, and 2687 manufactured by Nissin Chemical Industry Co., Ltd. Emulsions and the like are included.

(Composite resin particles)
The fine composite resin particles that can be contained in the precoating liquid are preferably fine composite resin particles obtained by emulsifying an acrylic resin with a urethane resin. That is, it is preferable that the fine composite resin particles have an inner layer made of an acrylic resin and a surface layer made of a urethane resin.

Here, the urethane resin exists at the interface between the acrylic resin as the water-insoluble resin fine particles and water as the continuous phase, and functions as a water-insoluble resin fine particle layer different from the resin that protects the water-insoluble resin fine particles.

By forming composite resin fine particles obtained by emulsifying acrylic resin with urethane resin in this way, unlike using acrylic resin alone, it is possible to suppress deterioration in compatibility with urethane resin and pigment flocculant. In addition, the physical properties of the image (coating film) can be improved and the stability of the precoat liquid can be improved as compared with emulsifying and mixing the acrylic resin and the urethane resin respectively.

In the composite resin fine particles obtained by emulsifying the acrylic resin in the urethane resin, the mass ratio (U/A) of the urethane resin (U) and the acrylic resin (A) is 40/60 to 95/5. is preferred. When the content of the urethane resin (U) is within the above range, the compatibility with the dispersant is improved, and the solvent resistance is also improved. Moreover, when the abundance of the acrylic resin (A) is within the above range, the adhesiveness to the acrylic film is excellent. In the above proportions, the mass ratio (U/A) between the urethane resin (U) and the acrylic resin (A) is preferably 40/60 to 80/20.

The total resin concentration of the acrylic resin and the urethane resin in the composite resin fine particles is not particularly limited, but is preferably 5.0% by mass or more, and is preferably 10.0 to 70.0% by mass. more preferred. When the resin concentration is within the above range, the fixability between the substrate and the ink is improved.

In addition, in emulsifying the acrylic resin with the urethane resin, a surfactant that acts as an emulsifier can be used together with the urethane resin. Here, by adding an emulsifier, the storage stability of the fine composite resin particles can be improved.

An anionic surfactant and a nonionic surfactant can be used as the emulsifier. In the present invention, it is preferable to use either one of the anionic surfactant and the nonionic surfactant, and it is more preferable to use both. Here, the total amount of the anionic surfactant and the nonionic surfactant is preferably 1.0 to 20.0 parts by mass with respect to 100 parts by mass of the total resin mass. Moreover, by setting the total amount of the anionic surfactant and the nonionic surfactant to be 20.0 parts by mass or less, the water resistance and solvent resistance can be improved.

Also, the blending mass ratio (X/Y) of the anionic surfactant (X) and the nonionic surfactant (Y) is preferably 100/0 to 50/50. By setting the blending amount of the anionic surfactant within the above range, emulsifiability and storage stability can be further improved.

Here, examples of anionic surfactants that can be used for emulsification include alkyl sulfates, polyoxyethylene alkyl ether sulfates, sulfosuccinates, alpha olefin sulfonates, N-acylamino acid salts, carboxylates, and phosphate esters. Among these, sulfosuccinates and alpha-olefin sulfonates are preferred.
In addition, examples of types of salts include, but are not particularly limited to, metal salts such as sodium salts, potassium salts, and magnesium salts, triethanolamine salts, and the like.

Examples of nonionic surfactants that can be used for emulsification include polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene alkylamine ethers, polyoxyethylene fatty acid esters, sorbitan fatty acid esters, Sugar fatty acid esters and the like are included. Among these, polyoxyethylene alkyl ethers and polyoxyethylene alkylphenyl ethers are preferred.

The average particle size of the composite resin fine particles described above is not particularly limited, but is preferably 10 to 500 nm, more preferably 10 to 300 nm, and even more preferably 10 to 200 nm. Measurement of the average particle size can be obtained by a commercially available particle size measuring instrument using dynamic light scattering method, electrophoresis method, etc., but measurement by dynamic light scattering method is simple and the particle size range can be determined. Accurate measurement is possible.

By using composite resin fine particles obtained by emulsifying an acrylic resin in a urethane resin, it is possible to improve the fixability of an image (coating film) on a low-absorbent base material or a non-absorbent base material.

Examples of commercially available resin fine particles used in the water-based ink according to the present invention are listed below.
(polyester resin)
Pesresin A-110F, A-520, A-613D, A-615GE, A-640, A-645GH, A-647GEX manufactured by Takamatsu Oil Co., Ltd., Elitel KA-5034, KA-5071S, KA-1449, KA manufactured by Unitika -0134, KA-3556, KA-6137, KZA-6034, KT-8803, KT-8701, KT-9204, KT-8904, KT-0507, KT-9511
(urethane resin)
NeoRez R-967, R-600, R-9671 manufactured by Kusumoto Kasei Co., Ltd. W-6061, W-5661, WS-4000 manufactured by Mitsui Chemicals
(acrylic resin)
Movinyl 6899D, 6969D, 6800, 6810 manufactured by Japan Coating Resin, TOCRYL W-7146, W-7150, W-7152 manufactured by Toyochem

(organic solvent)
A water-soluble organic solvent can be suitably used as the organic solvent contained in the water-based ink according to the present invention. Examples of water-soluble organic solvents include alcohols, polyhydric alcohols, amines, amides, glycol ethers, and 1,2-alkanediols having 4 or more carbon atoms.

Alcohols include, for example, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-1-propanol, t-butanol, 3-methoxy-1-butanol, 3-methoxy -3-methylbutanol, 1-octanol, 2-octanol, n-nonyl alcohol, tridecyl alcohol, n-undecyl alcohol, stearyl alcohol, oleyl alcohol, benzyl alcohol and the like.

Examples of polyhydric alcohols include ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol having 5 or more ethylene oxide groups, propylene glycol, dipropylene glycol, tripropylene glycol, and the number of propylene oxide groups. are 4 or more, polypropylene glycol, butylene glycol, hexanediol, pentanediol, glycerin, hexanetriol, thiodiglycol, and the like.

Examples of amines include ethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, morpholine, N-ethylmorpholine, ethylenediamine, diethylenediamine, triethylenetetramine, tetraethylenepentamine, polyethyleneimine, pentamethyldiethylenetriamine, tetramethylpropylenediamine, and the like.

Examples of amides include formamide, N,N-dimethylformamide, N,N-dimethylacetamide and the like.

Examples of glycol ethers include ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, and tripropylene glycol monomethyl. ether and the like.

Examples of 1,2-alkanediols having 4 or more carbon atoms include 1,2-butanediol, 1,2-pentanediol, 1,2-hexanediol, and 1,2-heptanediol. .

Organic solvents that are particularly preferably used are polyhydric alcohols, which can suitably suppress bleeding during high-speed printing. Specifically, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, dipropylene glycol, and tripropylene glycol are preferred.

The ink can contain one or a combination of two or more selected from these organic solvents.

The content of the organic solvent in the ink is not particularly limited, but is preferably within the range of 10-60% by mass.

(water, other additives)
Water contained in the ink according to the present invention is not particularly limited, and may be ion-exchanged water, distilled water, or pure water.

The ink according to the present invention may be used according to the purpose of improving surfactants, ejection stability, compatibility with print heads and ink cartridges, storage stability, image storage stability, and various other properties. Additives can be included.

The ink can also contain a surfactant. As a result, it is possible to improve the ink ejection stability and to control the spread (dot diameter) of droplets that have landed on the recording medium.

The surfactant that can be used in the ink according to the present invention can be used without any particular limitation. Nonionic or betaine types are preferred. In particular, in the present invention, when an alkaline component is contained in a surfactant such as an anionic surfactant, the aggregating property of the pigment is reduced, and the resin fine particles themselves tend to aggregate, so the surfactant is nonionic. things are preferred.

In the present invention, preferably fluorine-based or silicone-based surfactants with high static surface tension reducing ability, anionic surfactants such as dioctyl sulfosuccinate with high dynamic surface tension reducing ability, relatively low Nonionic surfactants such as molecular weight polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, acetylene glycols, Pluronic (registered trademark) type surfactants and sorbitan derivatives are preferably used. It is also preferable to use a fluorine-based or silicone-based surfactant in combination with a surfactant having a high dynamic surface tension-reducing ability.

The content of the surfactant in the ink is not particularly limited, but is preferably within the range of 0.1 to 5.0% by mass.

In the ink used in the present invention, in addition to those described above, depending on the purpose of improving ejection stability, compatibility with print heads and ink cartridges, storage stability, image storage stability, and other various performances, Various known additives such as polysaccharides, viscosity modifiers, resistivity modifiers, film-forming agents, UV absorbers, antioxidants, anti-fading agents, anti-mold agents, anti-rust agents, etc. are appropriately selected and used. For example, liquid paraffin, dioctyl phthalate, tricresyl phosphate, oil droplet fine particles such as silicone oil, described in JP-A-57-74193, JP-A-57-87988, JP-A-62-261476, etc. UV absorber, JP-A-57-74192, JP-A-57-87989, JP-A-60-72785, JP-A-61-146591, JP-A-1-95091, JP-A-3-13376, etc. anti-fading agent described in JP-A-59-42993, JP-A-59-52689, JP-A-62-280069, JP-A-61-242871, the fluorescence enhancer described in JP-A-4-219266, etc. A whitening agent etc. can be mentioned.

The ink used in the present invention having the above structure preferably has a viscosity of 1 to 40 mPa·s at 25° C., more preferably 2 to 10 mPa·s.

[4] Inkjet recording method In the inkjet recording method of the present invention, it is preferable to combine the precoat liquid and the water-based ink described above and use them as an inkjet recording liquid set. In the method using this inkjet recording liquid set, for example, one inkjet printer is used to apply the precoat liquid constituting the inkjet recording liquid set of the present invention to the surface of the non-absorbent substrate, and the ink and printing can be performed continuously and efficiently. In addition, it is possible to print characters, patterns, etc. with excellent image quality with little variation in dot diameter between substrates.

Specifically, the inkjet recording method of the present invention includes a precoat liquid application step of applying the precoat liquid onto the recording medium of the base material, and a precoat layer by drying the precoat liquid applied on the base material. an ink application step of applying the aqueous ink described above on the precoat layer by an inkjet method; and an ink drying step of drying the ink applied on the precoat layer to form an ink layer. and an image forming method comprising: Here, the precoat liquid application process and the ink application process may be performed simultaneously, or the ink application process may be performed immediately after the precoat liquid application process.

[4.1] Precoat Liquid Application Step In the precoat liquid application step, the precoat liquid described above is applied onto the recording medium of the low-absorbent base material or the non-absorbent base material.

The method of applying the precoat liquid onto the recording medium of the low-absorbent base material or non-absorbent base material is not particularly limited, but preferred examples include a roller coating method, a curtain coating method, a spray coating method, an inkjet method, and the like. can. Among them, the roller coating method is preferable from the viewpoint that a roller coating machine or the like can be connected to an inkjet device and used, and even if the viscosity is relatively high, the coating can be efficiently applied.
In addition, since the process of applying the pre-coating liquid is a process using an inkjet method, it is not necessary to apply a coagulant to the non-ink-coated area, so the coagulant that has not reacted with the ink is liberated and becomes cloudy. This is preferable in that such a situation does not occur.
In that case, as will be described later, if the substrate to be used is a metal substrate, etc., the metal substrate is placed on a conveying belt, and a precoat layer is applied while the belt is being conveyed, or a flat surface is used to fix the substrate. It is also preferable to use a bed-type printer for forming the precoat layer.

[4.2] Precoating Liquid Drying Step The precoating liquid drying step is a step of drying the precoating liquid applied on the recording medium of the low-absorbent base material or the non-absorbent base material to form a precoat layer. However, this step can be omitted, and a step of applying the ink liquid (ink applying step) may be performed continuously immediately after the precoat liquid applying step. Further, when the ink applying process is performed continuously in this way, or when the ink applying process is performed simultaneously with the precoat liquid applying process, drying of the precoat liquid is performed together with drying of the ink liquid.

The drying of the precoating liquid is preferably carried out under conditions that remove the solvent components of the precoating liquid, such as water and water-soluble organic solvents. The drying temperature of the precoat liquid is preferably in the range of 50 to 100°C, for example. The drying time of the precoat liquid is preferably, for example, within the range of 3 to 30 seconds.

Drying of the precoat liquid may be carried out, for example, using a non-contact heating drying device such as a drying oven or a hot air blower, or using a contact heating drying device such as a hot plate or a heat roller. you can go

The drying temperature is (a) when a non-contact heating drying device such as a drying furnace or hot air blower is used, the temperature in the furnace or the ambient temperature such as the hot air temperature, (b) a hot plate or a heat roller In the case of using a contact heating type drying apparatus such as, the temperature of the contact heating part or (c) the surface temperature of the surface to be dried is measured during the entire drying period of the precoat liquid. It is more preferable to measure (c) the surface temperature of the surface to be dried.

The thickness of the resulting precoat layer is preferably within the range of 0.3 to 3.0 μm, and more preferably within the range of 0.5 to 2 μm. When the thickness of the precoat layer is 0.3 μm or more, it is easy to improve the image adhesion and lamination strength while suppressing ink bleeding. When the thickness of the precoat layer is 3.0 μm or less, deformation stress due to moisture and heat can be reduced, so that image adhesion and lamination strength are less likely to be impaired.

[4.3] Ink application step In the ink application step, at the same time or immediately after forming the precoat layer on the recording medium of the low-absorbent substrate or the non-absorbent substrate, the ink of the inkjet recording liquid set described above is applied to the inkjet. It is a step of imparting according to the law.

The inkjet method is not particularly limited, and a printer equipped with an inkjet head loaded with ink can be used. Specifically, ink can be ejected as droplets from nozzles of an inkjet head based on a digital signal, and the droplets can be made to land on the precoat layer of the substrate for printing.

The inkjet head may be either an on-demand type or a continuous type. Examples of on-demand inkjet heads include electro-mechanical conversion, including single-cavity, double-cavity, bender, piston, shear mode and shared wall, as well as thermal inkjet and bubble jet ( "Bubble jet" includes electric-heat conversion methods including those of Canon Inc.'s registered trademark) type.

Among the above inkjet heads, an inkjet head (also called a piezo inkjet head) using a piezoelectric element as an electro-mechanical conversion element used in an electro-mechanical conversion system is preferable.

In addition, the inkjet head may be either a scanning type inkjet head or a single-pass type inkjet head, but the single-pass type is preferable. In the case of the single pass method, it is preferable to use a line head type inkjet head.

A line head type inkjet head is an inkjet head that has a length greater than the width of the printing range. As the line head type inkjet head, a single head having a width equal to or larger than the printing range may be used, or a plurality of heads may be combined to form an ink jet head having a width equal to or larger than the printing range.

In addition, a plurality of heads may be arranged side by side so that their nozzles are arranged in a zigzag arrangement to increase the resolution of the heads as a whole.

The conveying speed of the recording medium of the low-absorbent base material or the non-absorbent base material can be set, for example, within the range of 1 to 120 m/min. The faster the conveying speed, the faster the image forming speed. According to the present invention, a high-definition image with high ink fixability can be obtained even at a very high linear velocity of 50 to 120 m/min, which is applicable to a single-pass ink jet image forming method.

[4.4] Ink Drying Step In the ink drying step, the ink applied onto the recording medium of the low-absorbent base material or the non-absorbent base material is dried. When the precoating liquid drying process is omitted, the precoating liquid is also dried in the ink drying process.

The drying of the ink mainly removes water and water-soluble organic solvents, which are solvent components of the ink, and at the same time, dries the flocculant according to the present invention at a temperature equal to or higher than the thermal decomposition temperature to thermally decompose it. The upper limit of the drying temperature is preferably 220° C. or less from the viewpoint of achieving both the thermal decomposability of the coagulant and the stability of the ink composition. The drying time of the ink is controlled by at least the thermal decomposition time of the aggregating agent. The decomposition time is appropriately selected depending on the type of coagulant selected, and can be determined appropriately from the viewpoint of the degree of thermal decomposition at which the effects of the present invention are obtained and productivity.

The drying of the ink can be performed in the same manner as the drying of the precoat liquid described above.

[5] Ink Jet Recording Apparatus FIG. 1 is a schematic diagram of a precoat/ink jet recording apparatus preferred for the present invention. However, the present invention is not limited to this, and for example, in the precoat/inkjet recording apparatus 1 shown in FIG. 1, the first drying section 14 can be omitted.

The precoat/inkjet recording apparatus 1 is mainly composed of a precoat applying section 10 and an inkjet printing section 20 . The precoat layer C is formed on the base material F in the precoat applying section 10 , and the ink layer R is formed by the inkjet printing section 20 .

Specifically, precoat droplets 12 are ejected from the inkjet head 11 onto the base material F delivered from the delivery roller 30 to form the precoat layer C. Subsequently, the precoat layer C is dried by the first drying section 14 . Although the precoat application unit 10 shown in FIG. 1 is an inkjet head 11, it is not limited to this and may be a roll coater or the like.

Next, ink droplets 22 are ejected from the inkjet head 21 onto the precoat layer C to form an ink layer R, which is dried at a temperature equal to or higher than the thermal decomposition temperature of the flocculant according to the present invention by the second drying section 23. After that, the base material F on which the precoat layer C and the ink layer R are formed is wound up by the winding roller 40 to obtain an image recorded matter.

FIG. 1 shows the case where the substrate F is a film substrate, but in the case of a metal substrate, etc., the metal substrate is placed on a conveying belt, and the precoat layer C and the ink are mixed while conveying the belt. The layer R can be formed by coating in one pass.
In FIG. 1, the apparatus is configured to apply the water-based ink after applying the pre-coat liquid onto the base material, but the apparatus may be configured to apply the pre-coat liquid and the water-based ink at the same time.
Furthermore, as an apparatus other than the precoat/inkjet recording apparatus shown in FIG. 1, it is also preferable to use a flat bed type printer for applying the precoat liquid and the ink liquid. In flatbed printers, the substrate is fixed, and the inkjet head can be moved in the main scanning direction and the sub-scanning direction that intersects the main scanning direction, making it possible to print without transporting the substrate. is. Metal substrates such as tin plate cannot be conveyed from roll to roll unlike resin film substrates. Therefore, it is preferable to use a flatbed printer that does not need to convey the substrate.
Examples of such flatbed printers include the printers described in FIG. 1 of Japanese Patent Application Laid-Open No. 2015-74161 and FIG. 1 of Japanese Patent Application Laid-Open No. 2017-177578.

[6] Image Recorded Matter The image recorded matter according to the present invention comprises a base material, a precoat layer formed on the base material using the precoat liquid, and the water-based ink on the precoat layer. and an ink layer.

As shown in FIG. 2, the image recorded material P is formed by applying the precoat liquid according to the present invention onto the base material F with a roll coater or by ejecting it from an inkjet head to form a precoat layer C. An image recording layer R is formed by ejecting water-based ink from an inkjet head onto the position where the precoat layer C has been fixed and fixing it.

The above configuration shows the minimum configuration, and another functional layer may be formed between the base material and the precoat layer, and a non-absorbent ink layer may be formed on the ink layer via, for example, a laminate adhesive layer. A film substrate or the like may be laminated. At least, a configuration in which the precoat layer and the ink layer are in contact with each other is essential.

An example of the image recorded matter of the present invention is an image recorded matter using at least the precoating liquid and the aqueous ink of the present invention, wherein a first layer containing a thermosetting resin and the precoat are formed on a metal substrate. In a preferred embodiment, the second layer containing the liquid, the third layer containing the water-based ink, and the fourth layer containing the thermosetting resin are laminated in this order.

As specific examples of the image recorded matter, packaging materials for packaging canned food, retort food, beverages, etc. can be preferably mentioned.

FIG. 3 shows a cross-sectional view of a packaging material for canned food, which is an example of the image recorded matter of the present invention.
A thermosetting resin (for example, TW-1407 series, manufactured by T&K TOKA) is roller-coated on a tin substrate 51 to form a thermosetting resin layer (base coat) 52, and a precoat layer 53 and an ink layer 54 are formed thereon. to form an image. Next, a thermosetting resin (for example, AX-10 series manufactured by T&K TOKA) is applied with a roller to form a thermosetting resin layer (top coat) 55, which is then cured by heating and dried to form the canned food packaging material 50. Obtainable.

The present invention will be specifically described below with reference to examples, but the present invention is not limited to these. In the following examples, unless otherwise specified, operations were performed at room temperature (25°C). Moreover, unless otherwise specified, "%" and "parts" mean "% by mass" and "parts by mass" respectively.

[Resin Fine Particle Dispersion]
The glass transition point (Tg) and the average particle size of each resin fine particle in the commercially available resin fine particle dispersion liquids P1 to P9 shown in Table I below were measured, and the measurement results are shown in Table I below.
Next, in order to prepare a mixed solution containing 5% by mass of resin fine particles and 10 mmol/L of malonic acid, an aqueous malonic acid solution in which 20 mmol/L of malonic acid was dissolved in ion-exchanged water, Dilutions of the fine resin particle dispersions P1 to P9 shown in I were prepared with ion-exchanged water so that the solid content was 10% by mass.
Next, 10 ml of the malonic acid aqueous solution was added to 10 ml of the diluted solution while stirring to prepare mixtures A1 to A9 having a solid content of 5% by mass and a malonic acid content of 10 mmol/L.
Then, the pH of each mixed solution A1 to A9 at 25° C. and the average particle size of the fine resin particles in the mixed solution were measured. The measurement results of pH and average particle size are shown in Table I below.
The average particle size of each of the fine resin particles in the resin fine particle dispersions P1 to P9 and the mixed liquids A1 to A9 was measured by "Zetasizer 1000HS" manufactured by Marballoon.
In addition, the glass transition point (Tg) of the resin fine particles is measured by DSC (differential scanning calorimeter) in a temperature range of −30 to 200° C. at a heating rate of 10° C./min. It was identified by reading the glass transition temperature Tg from the peak.

[Preparation of precoat liquid]
0.5% by mass of malonic acid as a flocculating agent, 25% by mass of ethylene glycol, 0.5% by mass of surfactant KF351A (Shin-Etsu Silicone Co., Ltd.), and ion-exchanged water (remaining amount: amount to make the total amount 100% by mass) are stirred. The mixture was filtered through a 1 μm filter to obtain a precoat liquid 1.
Further, precoating liquids 2 to 14 were prepared in the same manner as in the preparation of precoating liquid 1, except that the type of flocculant and the amount of flocculant added were changed as described in II below.

[Ink preparation]
18% by mass of pigment (Pigment Blue 15:3), a pigment dispersant (acrylic dispersant having a sodium hydroxide-neutralized carboxyl group ("Joncryl 819" manufactured by BASF, acid value 75 mgKOH / g, solid 20% by mass), 20% by mass of ethylene glycol, and ion-exchanged water (remaining amount: amount to make the total amount 100% by mass). The zirconia beads of 50% by volume were dispersed using a sand grinder to prepare a pigment dispersion G-2 having a pigment content of 18% by mass.The average particle size of the pigment particles contained in this pigment dispersion The diameter was 110 nm, and the average particle size was measured using "Zetasizer 1000HS" manufactured by Maruballoon.

To 27.8% by mass of the pigment dispersion (5% by mass as a solid content), the commercially available resin fine particle dispersion P1 (the amount added is such that the resin fine particles (solid content) in the ink is 5% by mass. adjustment), 30% by mass of ethylene glycol, 0.5% by mass of surfactant KF351A (Shin-Etsu Silicone Co., Ltd.), and ion-exchanged water (remaining amount; total amount is 100% by mass) are added with stirring, and the resulting mixture Ink 1 was obtained by filtering the liquid through a 1 μm filter. There was no substantial compositional change before and after filtration.
Further, Inks 2 to 9 were prepared in the same manner as Ink 1, except that the type of the commercially available fine resin particle dispersion before the addition of malonic acid was changed as shown in Table II below.

[Print]
The precoating liquids 1 to 14 and inks 1 to 9 prepared above were used in the combinations shown in Table II below to print as follows.
Two Konica Minolta independently driven inkjet heads (360 dpi, ejection volume 14 pL) were arranged side by side so that the nozzles were staggered to produce a head module capable of printing a 720 dpi x 720 dpi solid image in a single pass. . Two such head modules were prepared and arranged side by side along the transport direction of a transport stage that transports the recording medium. Each head module was installed so as to intersect with the transport direction (moving axis of the transport stage). In this manner, a printing rate of 200%, that is, an amount of ink applied for two colors (22.5 cc/m ² ) can be printed in one pass of the recording medium.
Of these two head modules, the head module that is located on the front side in the transport direction and prints on the recording medium first is filled with the precoat liquid prepared above, and the head module that is located on the rear side in the transport direction and prints on the recording medium later. The ink prepared above was put into the head module for printing.
Then, a PET film (FE2001, thickness 50 μm, manufactured by Futamura Chemical Co., Ltd.) was prepared as a recording medium on the transport stage, and transported at a speed of 20 m/min. The precoat liquid and ink were printed at .
At that time, the pre-coating liquid had a printing rate of 25%, and the ink had a printing rate of 100%.
In addition, a PET film recording medium similar to that described above was separately prepared, and a straight line with a width of 3 dots and a width of 106 μm was printed on the recording medium with the precoating liquid and the ink. After printing, the recording medium was placed in a dryer set at 90° C. and dried for 5 minutes to obtain an image record.

[evaluation]
<Glossiness>
Of the two types of image recorded matter obtained above, the one on which the ink was printed on the entire surface was used, and the glossiness was visually evaluated according to the following index.
◎: Highly glossy on the entire surface 〇: Slightly low gloss △: Low gloss, no gloss ×: No gloss at all, matte

<Adhesion>
Of the two kinds of image recorded matter obtained above, the one on which the ink was printed on the entire surface was used, and the printed surface was rubbed with a fingernail, and the adhesion was evaluated according to the following indices.
◎: Printed surface does not change and cannot be removed by rubbing with fingernail 〇: Scratched with fingernail, but does not come off △: Scratched with fingernail, printed surface partially peeled off ×: Nail The printed surface will come off when rubbed

<bleeding>
Of the two kinds of image recorded matter obtained above, the one on which fine lines were printed with ink was used, and bleeding was visually evaluated according to the following index.
⊚: Thin lines are printed in a straight line. ◯: Fine lines are slightly swollen when viewed closely.
×: The line is greatly blurred and thickly distorted

As shown in the above results, as in the present invention, a mixture prepared by adding an aqueous malonic acid solution to a resin fine particle dispersion liquid so that the resin fine particles are 5% by mass and the malonic acid is 10 mmol/L. By using a resin fine particle dispersion having a pH of 5 or less at 25° C. in the liquid, the glossiness of the image recorded matter is good, and fine line printing is also good, and the image quality can be improved. Do you get it. Also, the adhesiveness was good.

The present invention can be used for an inkjet recording method capable of improving image quality and having good adhesion.

1 precoat/inkjet recording device 10 precoat imparting unit 11 inkjet head 12 precoat droplet 14 first drying unit 20 IJ print unit 21 inkjet head 22 ink droplet 23 second drying unit 30 delivery roller 40 winding roller C precoat layer F base Material P Image recorded matter R Ink layer 50 Packaging material for canned food 51 Tin substrate 52 Thermosetting resin layer (base coat)
53 precoat layer 54 ink layer 55 thermosetting resin layer (top coat)

Claims (10)

1. An inkjet recording method in which a water-based ink is printed and dried at the same time or immediately after applying a precoat liquid to a substrate,
   the precoat liquid contains an organic acid or a polyvalent metal salt,
   the water-based ink contains a pigment, a fine resin particle dispersion, water, and an organic solvent, and
   An inkjet recording method in which the fine resin particle dispersion satisfies the following condition (I).
   Condition (I): In a mixed solution prepared by adding an aqueous malonic acid solution to the fine resin particle dispersion so that the fine resin particles are 5% by mass and the malonic acid is 10 mmol/L, the pH at 25° C. is 5 or less.
2. The inkjet recording method according to claim 1, wherein the fine resin particles do not aggregate in the mixed liquid.
3. The resin fine particles contained in the resin fine particle dispersion liquid are acrylic resin fine particles, urethane resin fine particles, or polyester resin fine particles, and
   3. The ink jet recording method according to claim 1, wherein the average particle diameter is 200 nm or less.
4. The inkjet recording method according to any one of claims 1 to 3, wherein the pigment is a self-dispersing pigment having an anionic group on its surface.
5. The inkjet recording method according to any one of claims 1 to 3, wherein the pigment is dispersed with an anionic polymer dispersant.
6. The ink jet recording method according to any one of claims 1 to 3, wherein the pigment is dispersed with its surface coated with an anionic resin.
7. The inkjet recording method according to any one of claims 1 to 6, wherein the inkjet recording method is a single pass system.
8. The inkjet recording method according to any one of claims 1 to 7, wherein the precoat liquid is applied to the substrate by an inkjet method.
9. 9. The organic acid according to any one of claims 1 to 8, wherein the organic acid has a first dissociation constant pK _a1 of 1.5 to 4 at a temperature of 25°C. Inkjet recording method.
10. 10. Any one of claims 1 to 9, wherein the polyvalent metal salt contains a polyvalent metal salt selected from calcium chloride, magnesium chloride, calcium nitrate, magnesium nitrate, and calcium salts and magnesium salts of carboxylic acids. The ink jet recording method according to the item.

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