JP2024059573A - Water-based ink, ink-jet recording method, and ink-jet recording apparatus - Google Patents

Abstract

[Problem] To provide an aqueous inkjet ink that has the abrasion resistance required in the commercial printing and industrial printing fields and is capable of recording images with reduced change in glossiness when a recording material is loaded and the recording surface is rubbed. [Solution] The aqueous inkjet ink contains a wax, (i) a nonionic dispersant for dispersing the wax, and (ii) an anionic dispersant. The nonionic dispersant is a compound represented by general formula (1) and has an HLB value of 9.0 or more and 18.0 or less. The anionic dispersant is a compound having at least one anionic group selected from the group consisting of a sulfonic acid group, a carboxylic acid group, and a phosphoric acid group. R1-O-(R2O)n-H ... (1) (In the general formula (1), R1 represents an alkyl group or an alkenyl group having 4 or more and 40 or less carbon atoms. Each R2 independently represents an ethylene group, a propylene group, or a butylene group. n represents the number of moles of alkylene oxide added and is 3 or more and 50 or less.) [Selected Figure] None

Description

The present invention relates to an aqueous ink, an inkjet recording method, and an inkjet recording device.

Inkjet recording methods make it possible to record on a variety of recording media. In order to obtain better images, various inks have been proposed depending on the purpose, such as inks suitable for recording photographic quality images on glossy paper, and inks suitable for recording text on plain paper.

In recent years, the market has been demanding inkjet recording not only on specialized recording media such as plain paper and glossy paper that have traditionally been used for inkjet printing, but also on papers that have traditionally been used for offset printing (coated paper, uncoated paper, printing paper, etc.). In other words, there is a strong demand for the development of inkjet technology that excels in high-mix, small-lot printing in the commercial and industrial printing fields where offset printing has been mainstream.

Under these circumstances, there is a demand for image quality that far surpasses that of conventional inkjet recording, as well as high abrasion resistance comparable to offset printing.

For example, Patent Document 1 proposes a technique for improving the scratch resistance of an image by adding a water-soluble resin to the ink, and Patent Document 2 proposes a technique for agglomerating and fixing the ink by using a reaction liquid together with the ink. Patent Documents 3 and 4 also propose techniques for improving the scratch resistance of an image by adding wax to the ink or reaction liquid to improve slipperiness.

JP 2015-199788 A JP 2018-53124 A JP 2010-155359 A JP 2019-203044 A

The inventors have examined whether the methods described in Patent Documents 1 to 4 can produce images with abrasion resistance equivalent to that of offset printing, which has been in demand in recent years.

It has been found that the method described in Patent Document 1 makes it difficult to produce an image with the same abrasion resistance as offset printing. This is because coated paper used in offset printing does not have a fixing layer like inkjet paper, and the ink layer is easily peeled off when rubbed with strong force.

The method described in Patent Document 2 also did not achieve the abrasion resistance of images required for offset printing paper.

Furthermore, it was found that the methods described in Patent Documents 3 and 4 cause another problem. That is, in the commercial printing and industrial printing fields, recorded images (hereinafter also referred to as records) are sometimes stacked on top of each other. In this case, the recorded surface of a record is rubbed against the recorded surface or unrecorded portion (non-recorded portion) of a record stacked opposite it. As a result, it was recognized that a new problem occurs in that the glossiness of the recorded surface changes, reaching a level that is unacceptable as a record.

Therefore, the object of the present invention is to provide an inkjet water-based ink that has the abrasion resistance required in the commercial and industrial printing fields and is capable of recording images with reduced change in glossiness when a recording material is loaded and the recording surface is rubbed. Another object of the present invention is to provide an inkjet recording method and an inkjet recording device that use this water-based ink.

That is, according to the present invention, there is provided an aqueous ink for inkjet recording, which contains a wax, (i) a nonionic dispersant for dispersing the wax, and (ii) an anionic dispersant, wherein the nonionic dispersant is a compound represented by the following general formula (1) and has an HLB value of 9.0 or more and 18.0 or less, and the anionic dispersant is a compound having at least one anionic group selected from the group consisting of a sulfonic acid group, a carboxylic acid group, and a phosphate group.
R ¹ -O-(R ² O) _n -H ... (1)
(In the general formula (1), ^R1 represents an alkyl group or an alkenyl group having 4 or more and 40 or less carbon atoms. Each ^R2 independently represents an ethylene group, a propylene group, or a butylene group. n represents the number of moles of alkylene oxide added and is 3 or more and 50 or less.)

According to the present invention, it is possible to provide an aqueous inkjet ink that has the abrasion resistance required in the commercial and industrial printing fields, and is capable of recording images with reduced change in glossiness when recorded matter is stacked and the recording surface is rubbed. In addition, according to the present invention, it is possible to provide an inkjet recording method and an inkjet recording device that use this aqueous ink.

FIG. 1 is a schematic diagram illustrating an embodiment of an inkjet recording apparatus of the present invention. FIG. 2 is a perspective view showing an example of a liquid application device.

The present invention will be described in more detail below with reference to preferred embodiments. In the present invention, when the compound is a salt, the salt is present in the ink in the form of dissociation into ions, but for convenience, it is expressed as "containing a salt". In addition, the aqueous ink for inkjet printing and the reaction liquid may be simply referred to as "ink" and "reaction liquid". Unless otherwise specified, the physical property values are values at room temperature (25°C). When "(meth)acrylic acid" and "(meth)acrylate" are written, they mean "acrylic acid, methacrylic acid" and "acrylate, methacrylate", respectively. In the present invention, the "unit" constituting the resin means a repeating unit derived from one monomer.

First, the inventors conducted a detailed study on the scratch resistance of images in recorded matter. When performing inkjet recording on paper used in offset printing, one of the requirements for improving the scratch resistance of images is to include wax in the ink.

When adding wax to an aqueous inkjet ink, it is necessary to impart suitable dispersibility to the aqueous medium. There are no particular limitations on the method for doing so. Those skilled in the art can impart dispersibility to the wax in the aqueous medium using known methods. Details of the method will be described later.

The inventors added various waxes (hereinafter, sometimes simply referred to as waxes) that were made dispersible in aqueous media to inkjet inks and investigated the scratch resistance of images. As a result, they concluded that the scratch resistance of images can reach the level required in recent years, regardless of the type of dispersant used to make the wax dispersible.

Furthermore, the inventors conducted a more stringent evaluation assuming offset printing. Specifically, they conducted a test in which another recording medium was placed in close contact with the recording surface of a recording medium on which inkjet recording had been performed, and the two recording media were rubbed together. As a result, they found that the glossiness of the recording surface can change depending on the type and amount of dispersant used to impart dispersibility to the wax. Specifically, they found that when an anionic dispersant or a nonionic dispersant was used alone, the change in glossiness of the recording surface was significant. They conducted a more detailed study of this phenomenon and speculated that the reason for this is as follows.

[Reasons for changes in gloss]
First, a detailed study was conducted on the case where an anionic dispersant was used alone as a dispersant for wax. A water-based ink containing wax was applied to a recording medium by an inkjet recording method to record an image, thereby producing a recorded matter. When the produced recorded matter was brought into close contact with another recording medium and rubbed together, the glossiness of the recorded surface changed. According to the study by the present inventors, it is believed that the following phenomenon occurs in the area where the glossiness has changed.

It is believed that the wax behaves as follows on the recording surface where water-based ink has been recorded. On recording media without a receptive layer, it was observed using a scanning electron microscope (SEM) that the wax was present with its head protruding from the ink layer when the ink was fixed. This is consistent with the improvement in the slipperiness of the surface of a recording created using an ink containing wax, which reaches the required level of abrasion resistance.

On the other hand, when the wax protruding from the surface of the ink layer is rubbed against another recording medium in close contact with the recording surface, the following is thought to occur. That is, the top of the wax is scraped off by rubbing against the other recording medium, leaving a flat surface. A flat surface reflects more of the incoming light, which is thought to result in a change in the glossiness.

Furthermore, it is speculated that in waxes that use anionic dispersants, the change in gloss becomes more pronounced for the following reasons. For example, when the anionic dispersant is a carboxylate, the carboxylate is ionized and exhibits dispersibility in an aqueous medium. More specifically, it is believed that the anionic dispersant ionizes, and the positively charged portion interacts with the wax, while the negatively charged portion interacts with the aqueous medium, resulting in the wax exhibiting a stable dispersion state.

However, due to the properties of anionic dispersants, they interact with multiple waxes at once, causing the waxes to settle close to each other. This means that the waxes tend to form a sea-island structure on the recording medium when they are close to each other. The inventors speculate that when this sea-island structure is formed, the upper part of the wax is scraped off as described above, resulting in a state in which more of the incident light is reflected, which is why the change in gloss is noticeable.

Next, we also investigated the case where a nonionic dispersant was used alone as a wax dispersant. It is believed that the dispersion stability of wax dispersed with a nonionic dispersant is slightly lower than that of wax dispersed with an anionic dispersant. It was found that wax with reduced dispersion stability is more likely to be unevenly distributed on the recording surface. In other words, it is believed that the wax tends to have an island-sea structure, and as a result, it is presumed that changes in gloss occur even when a nonionic dispersant is used alone.

[Reasons why changes in gloss can be suppressed]
The present inventors have found that by using an ink containing a wax dispersed by using a specific nonionic dispersant and an anionic dispersant in combination, it is possible to achieve both abrasion resistance of an image and suppression of changes in glossiness. The present inventors speculate that the reason for this is as follows.

As the anionic dispersant, a compound having at least one anionic group selected from the group consisting of a sulfonic acid group, a carboxylic acid group, and a phosphoric acid group is used. As the nonionic dispersant, a compound represented by the following general formula (1) having an HLB value of 9.0 to 18.0 is used. This compound is generally called polyoxyalkylene alkyl ether or polyoxyalkylene alkenyl ether. The wax dispersed by using these specific nonionic dispersants and anionic dispersants in combination exists on the surface of the recorded material with its head protruding from the surface of the recorded material, as described above, and it is considered that the slipperiness is guaranteed.
R ¹ -O-(R ² O) _n -H ... (1)
(In the general formula (1), ^R1 represents an alkyl group or an alkenyl group having 4 or more and 40 or less carbon atoms. Each ^R2 independently represents an ethylene group, a propylene group, or a butylene group. n represents the number of moles of alkylene oxide added and is 3 or more and 50 or less.)

Furthermore, with regard to the change in glossiness of the image, it is speculated that the presence of the specific nonionic dispersant mentioned above results in the following state:

When the dispersant used to disperse the wax is only an anionic dispersant, the anionic dispersant interacts with multiple waxes at once, resulting in the waxes coming closer to each other, forming a so-called sea-island structure. In contrast, by using the specific nonionic dispersant in combination, the waxes are less likely to come close to each other, making it difficult to form a sea-island structure. Specifically, the presence of the polyoxyalkylene portion contained in the molecular structure of the specific nonionic dispersant in the vicinity of the wax makes it possible to suppress the waxes coming closer to each other through the anionic dispersant. In other words, the waxes do not come too close to each other, and can exist in a dispersed state within the recording surface.

As a result, the change in glossiness of the image caused by contact with the recording medium and rubbing against it is thought to be less noticeable because it is less likely to form a sea-island structure on the recording medium and is dispersed within the surface, even if the wax itself is scraped off and the surface becomes flat, increasing the amount of reflected light. As a result, it is possible to suppress the change in glossiness.

It was also found that the following secondary effects could be obtained. That is, when a wax dispersed by using the above-mentioned specific nonionic dispersant and anionic dispersant in combination is used, the wax can be dispersed and present on the recording surface. As a result, the inventors' study revealed that the slipperiness caused by the wax is not unevenly distributed on the recording surface, but is uniformized, and the scratch resistance of the image is at a much higher level. As a result of further study by the inventors, it was found that the above-mentioned effect cannot be obtained when a compound corresponding to the above-mentioned nonionic dispersant is added to an ink containing a wax dispersed by an anionic dispersant. It was also found that the above-mentioned effect cannot be obtained when a compound corresponding to the above-mentioned anionic dispersant is added to an ink containing a wax dispersed by a nonionic dispersant. In other words, it is important in the present invention to use a wax dispersed by both a specific nonionic dispersant and an anionic dispersant.

As described above, the nonionic dispersant has an HLB value of 9.0 or more and 18.0 or less. By setting the HLB value within the above range, the hydrophilicity and hydrophobicity of the nonionic dispersant are balanced, and the approach of waxes to each other that occurs via the anionic dispersant can be suppressed. If the HLB value is outside the above range (less than 9.0 or more than 18.0), the balance of the hydrophilicity and hydrophobicity of the nonionic dispersant is lost, making it difficult for the nonionic dispersant to exist near the wax, and the approach of waxes to each other cannot be suppressed. Details of the HLB value will be described later.

<Ink>
The ink of the present invention is an aqueous inkjet ink containing particles (wax particles) formed of wax, and the wax particles are wax dispersed in both a specific nonionic dispersant and an anionic dispersant. Each component used in the ink will be described in detail below.

(Wax particles)
The ink contains wax particles in which wax is dispersed in both a nonionic dispersant and an anionic dispersant. The wax particles are particles formed of wax. That is, the ink contains, in addition to wax, a nonionic dispersant and an anionic dispersant for dispersing the wax. The wax referred to here may be a composition containing components other than wax, or may be wax itself.

In the narrow sense, wax is an ester of a water-insoluble higher monohydric or dihydric alcohol and a fatty acid, and includes animal waxes and vegetable waxes, but does not include oils and fats. In the broad sense, wax includes high melting point fats, mineral waxes, petroleum waxes, and blends and modified products of various waxes. In the present invention, any wax in the broad sense can be used without particular restrictions. Wax in the broad sense can be classified into natural waxes, synthetic waxes, blends of these (blended waxes), and modified products of these (modified waxes).

Examples of natural waxes include animal waxes such as beeswax, spermaceti, and wool wax (lanolin); vegetable waxes such as wood wax, carnauba wax, sugarcane wax, palm wax, candelilla wax, and rice wax; mineral waxes such as montan wax; and petroleum waxes such as paraffin wax, microcrystalline wax, and petrolatum. Examples of synthetic waxes include hydrocarbon waxes such as Fischer-Tropsch wax and polyolefin wax (e.g., polyethylene wax, polypropylene wax). The blended wax is a mixture of the above-mentioned various waxes. The modified wax is a wax obtained by modifying the above-mentioned various waxes through oxidation, hydrogenation, alcohol modification, acrylic modification, urethane modification, or the like. For example, oxidized polyolefins are obtained by oxidizing polyolefins, and may be synthesized by oxidizing polyolefins, or commercially available products may be used. For example, such oxidized polyolefins include oxidized polyethylene wax and oxidized polypropylene wax, which are oxides of polyolefin waxes. One of the above waxes may be used alone, or two or more may be used in combination. The wax is preferably at least one selected from the group consisting of microcrystalline wax, Fischer-Tropsch wax, polyolefin wax, paraffin wax, and modified or blended products thereof. Of these, a blend of multiple types of wax is more preferable, and a blend of petroleum wax and synthetic wax is particularly preferable.

The wax is preferably solid at room temperature (25°C). The melting point (°C) of the wax is preferably 40°C or higher and 120°C or lower, and more preferably 50°C or higher and 100°C or lower. The melting point of the wax can be measured in accordance with the test method described in 5.3.1 (melting point test method) of JIS K2235:1991 (petroleum wax). In the case of microcrystalline wax, petrolatum, and a mixture of multiple types of wax, the test method described in 5.3.2 can be used to measure more accurately. The melting point of the wax is easily affected by characteristics such as molecular weight (the higher the molecular weight, the higher the melting point), molecular structure (the higher the melting point if the chain is straight, and the lower the melting point if the chain is branched), crystallinity (the higher the crystallinity, the higher the melting point), and density (the higher the crystallinity, the higher the melting point). Therefore, by controlling these characteristics, it is possible to obtain a wax having a desired melting point. The melting point of the wax in the ink can be measured in accordance with the above test method, for example, after the ink is subjected to ultracentrifugation, the wax separated is washed and dried.

The content (mass %) of wax in the ink is preferably 0.30% by mass or more and 8.00% by mass or less, and more preferably 0.50% by mass or more and 4.00% by mass or less, based on the total mass of the ink. The total content (mass %) of wax and dispersants for dispersing wax (nonionic dispersant and anionic dispersant) in the ink is preferably 0.50% by mass or more and 10.00% by mass or less, based on the total mass of the ink. Of these, it is more preferable that it is 0.50% by mass or more and 9.00% by mass or less, and even more preferable that it is 1.00% by mass or more and 5.00% by mass or less. Here, the dispersant for dispersing wax refers to (i) nonionic dispersant and (ii) anionic dispersant, which will be described later.

(Wax dispersant)
[Nonionic dispersant]
The nonionic dispersant for dispersing wax is a compound represented by the following general formula (1). This compound is also called polyoxyalkylene alkyl ether or polyoxyalkylene alkenyl ether. Hereinafter, alkyl ether and alkenyl ether will be collectively referred to as alkyl ether for convenience. The HLB value of the nonionic dispersant is 9.0 or more and 18.0 or less.
R ¹ -O-(R ² O) _n -H ... (1)
(In the general formula (1), ^R1 represents an alkyl group or an alkenyl group having 4 or more and 40 or less carbon atoms. Each ^R2 independently represents an ethylene group, a propylene group, or a butylene group. n represents the number of moles of alkylene oxide added and is 3 or more and 50 or less.)

^R1 represents an alkyl group or an alkenyl group, and has 4 to 40 carbon atoms. ^R2 each independently represents an ethylene group, a propylene group, or a butylene group. Among these, an ethylene group or a propylene group is preferable. n represents the number of moles of alkylene oxide added, and is 3 to 50.

The "HLB value" of a surfactant in this specification is a value determined by the Griffin method, and is calculated based on the formula: HLB value = 20 x (formula weight of hydrophilic group of surfactant) / (molecular weight of surfactant). The HLB value determined by the Griffin method is a physical property value that indicates the degree of hydrophilicity or lipophilicity of a surfactant, and takes a value between 0 and 20. The smaller the HLB value, the higher the lipophilicity, and the higher the HLB value, the higher the hydrophilicity.

Examples of polyoxyalkylene alkyl ethers include polyoxyethylene alkyl ethers (general formula (2): R ¹ -O-(C ₂ H ₄ O) _n -H), polyoxypropylene alkyl ethers (general formula (3): R ¹ -O-(C ₃ H ₆ O) _n -H), polyoxyethylene-polyoxypropylene alkyl ethers (general formula (4): R ¹ -O-[(C ₂ H ₄ O) _n1 -(C ₃ H ₆ O) _n2 ]-H), and polyoxybutylene alkyl ethers (general formula (5): R ¹ -O-(C ₄ H ₈ O) _n -H). Among these, polyoxyethylene alkyl ethers and polyoxypropylene alkyl ethers are preferred. One of these nonionic dispersants may be used alone, or two or more may be used in combination. As described above, ^R1 in the above general formulas (2) to (5) represents an alkyl group or an alkenyl group, and n (including n1 and n2, which are independent of each other) represents the number of moles of alkylene oxide (ethylene oxide, propylene oxide, or butylene oxide) added (the number of repeating units).

Examples of polyoxyethylene alkyl ethers include polyoxyethylene lauryl ether, polyoxyethylene tridecyl ether, polyoxyethylene myristyl ether, polyoxyethylene cetyl ether, polyoxyethylene oleyl ether, polyoxyethylene stearyl ether, polyoxyethylene isostearyl ether, polyoxyethylene behenyl ether, and polyoxyethylene octyldodecyl ether.

Examples of polyoxypropylene alkyl ethers include polyoxypropylene butyl ether, polyoxypropylene myristyl ether, polyoxypropylene cetyl ether, and polyoxypropylene stearyl ether.

Examples of polyoxyethylene-polyoxypropylene alkyl ethers include polyoxyethylene-polyoxypropylene butyl ether, polyoxyethylene-polyoxypropylene lauryl ether, polyoxyethylene-polyoxypropylene cetyl ether, and polyoxyethylene-polyoxypropylene stearyl ether.

Among polyoxyalkylene alkyl ethers, polyoxyethylene alkyl ethers are preferred. In other words, the nonionic dispersant is preferably a compound represented by the following general formula (2). When polyoxyethylene alkyl ether and an anionic dispersant are used in combination with each other and applied to wax, uneven distribution of the wax on the recording surface is easily suppressed, the wax is made to exist more uniformly on the recording medium, and changes in glossiness can be efficiently suppressed.
R ¹ -O-(C ₂ H ₄ O) _n -H ... (2)
(In the general formula (2), ^R1 represents an alkyl group or an alkenyl group having 4 or more and 40 or less carbon atoms. n represents the number of moles of alkylene oxide added and is 3 or more and 50 or less.)

In addition, it is more preferable that the number of moles of alkylene oxide added in the polyoxyalkylene alkyl ether is 10 or more, since this effectively suppresses changes in glossiness. The alkylene oxide may be called an alkylene oxide group, an oxyalkylene group, a polyoxyalkylene chain, a polyalkylene oxide chain, or the like. The number of moles of alkylene oxide added is the number of repeating units of ethylene oxide, propylene oxide, butylene oxide, or the total of these. It is preferable that the number of moles of alkylene oxide added is 40 or less.

Furthermore, the hydrocarbon group represented by R ¹ in the above general formulas (2) to (4) may be either linear or branched, and may be either saturated or unsaturated. It is more preferable that the number of carbon atoms in the hydrocarbon group represented by R ¹ is 5 to 30. By having the carbon number of the hydrocarbon group be 5 to 30, it is easy to inhibit the interaction of the wax particles caused by the anionic dispersant used in combination, and to suppress uneven distribution of the wax on the surface of the recorded material. Therefore, it is easy to efficiently suppress changes in the glossiness of the image. It is particularly preferable that the carbon number of the hydrocarbon group represented by R ¹ is 8 to 30.

Here, the nonionic dispersant is preferably a nonionic surfactant. A surfactant is a substance that is composed of a hydrophobic portion (such as a hydrocarbon chain, a perfluoroalkyl group, a siloxane structure, etc.) and a hydrophilic portion (such as an ethylene oxide group). In other words, even if the nonionic dispersant is a compound represented by general formula (1), it is preferable that it does not contain a water-soluble organic solvent (for example, triethylene glycol monobutyl ether in which R ¹ has 4 carbon atoms and n is 3, or tetraethylene glycol monobutyl ether in which R ¹ has 4 carbon atoms and n is 4).

The molecular weight of the nonionic surfactant is preferably 280 or more, and more preferably 300 or more. The molecular weight is preferably 3,000 or less, more preferably 2,500 or less, and particularly preferably 2,000 or less.

The content (mass %) of the nonionic dispersant in the ink is preferably 0.01% by mass or more and 2.50% by mass or less, based on the total mass of the ink, and more preferably 0.10% by mass or more and 2.50% by mass or less. Of these, 0.30% by mass or more and 1.50% by mass or less is particularly preferable.

[Anionic dispersant]
The anionic dispersant is a compound having at least one anionic group selected from the group consisting of a sulfonic acid group, a carboxylic acid group, and a phosphoric acid group. Of these, the anionic group in the anionic dispersant is preferably a carboxylic acid group.

The inventors speculate that the reason why it is preferable for the anionic group in the anionic dispersant to be a carboxylic acid group is as follows. An anionic dispersant having a carboxylic acid group can form hydrogen bonds with a nonionic dispersant used in combination, either directly or via the water in the ink. As a result, the fixing position of the wax dispersed by the dispersant can be made more random, making it difficult for a sea-island structure to form. As a result, it is believed that changes in the glossiness of the image can be effectively suppressed.

As the anionic dispersant having an anionic group, an anionic surfactant or a resin having an anionic functional group can be suitably used. Specific examples of anionic surfactants include carboxylates, sulfonates, sulfates, and phosphates. Examples include linear higher carboxylic acids (salts), sulfonic acids (salts), alkylbenzenesulfonates, alkyl sulfates, polyoxyethylene alkyl sulfates, alkyl phosphates, and resins having an anionic functional group. Specific examples include montanic acid, isomerized linoleic acid, and salts thereof.

As a resin having an anionic functional group, for example, an ethylene acrylic acid copolymer can be suitably used. In particular, the anionic dispersant having an anionic group is preferably a resin having an anionic group, and more preferably an ethylene acrylic acid copolymer. By using an ethylene acrylic acid copolymer, the dispersibility of the wax is improved, and at the same time, the combined effect with the nonionic dispersant is enhanced, and uneven distribution of the wax on the recording surface is suppressed, thereby suppressing gloss changes to a higher level.

The content (mass %) of the anionic dispersant in the ink is preferably 0.01% by mass or more and 2.50% by mass or less, and more preferably 0.02% by mass or more and 2.00% by mass or less, based on the total mass of the ink. Of these, 0.04% by mass or more and 1.50% by mass or less is particularly preferred.

The total content (mass %) of the nonionic dispersant and the anionic dispersant in the ink is preferably 0.15 to 0.50 times the mass ratio of the wax content (mass %). By setting the mass ratio at 0.15 or more, sufficient dispersion stability of the wax can be obtained, and changes in the glossiness of the image can be suppressed to a higher level. On the other hand, by setting the mass ratio at 0.50 or less, the dispersion stability of the wax can be maintained while suppressing sinking of the wax into the recording medium, thereby further improving the scratch resistance of the image.

The content (mass %) of the anionic dispersant in the ink is preferably 0.10 to 0.50 times the content (mass %) of the nonionic dispersant. By setting the mass ratio within the above range, the wax is stably dispersed while inhibiting the interaction of the wax particles caused by the anionic dispersant used in combination, making it easier to suppress uneven distribution of the wax on the recording medium surface. Therefore, changes in the glossiness of the image can be suppressed to a higher level.

(Coloring material)
The ink preferably contains a coloring material. A pigment or a dye can be used as the coloring material. The content (mass %) of the coloring material in the ink is preferably 0.5 mass % or more and 15.0 mass % or less, and more preferably 1.0 mass % or more and 10.0 mass % or less, based on the total mass of the ink.

Specific examples of pigments include inorganic pigments such as carbon black and titanium oxide; and organic pigments such as azo, phthalocyanine, quinacridone, isoindolinone, imidazolone, diketopyrrolopyrrole, and dioxazine. One type of pigment may be used alone, or two or more types may be used in combination.

As a method for dispersing pigments, resin-dispersed pigments using resin as a dispersant, self-dispersed pigments in which hydrophilic groups are bonded to the pigment particle surface, etc. can be used. In addition, resin-bonded pigments in which organic groups containing resin are chemically bonded to the pigment particle surface, and microcapsule pigments in which the pigment particle surface is coated with resin, etc. can be used. It is also possible to use a combination of pigments with different dispersion methods among these. In the present invention, it is preferable to use resin-dispersed pigments in which a resin as a dispersant is physically adsorbed onto the pigment particle surface, and self-dispersed pigments in which hydrophilic groups are bonded to the pigment particle surface, rather than resin-bonded pigments or microcapsule pigments.

As a resin dispersant for dispersing the pigment in an aqueous medium, it is preferable to use one that can disperse the pigment in an aqueous medium by the action of anionic groups. As a resin dispersant, a resin having an anionic group can be used, and it is preferable to use a resin such as that described below, especially a water-soluble resin. The pigment content (mass %) in the ink is preferably 0.3 to 10.0 times the mass ratio of the resin dispersant content (mass %).

As the self-dispersing pigment, one in which an anionic group is bonded to the particle surface of the pigment directly or via another atomic group (-R-) can be used. Specific examples of the other atomic group (-R-) include linear or branched alkylene groups having 1 to 12 carbon atoms; arylene groups such as phenylene groups and naphthylene groups; carbonyl groups; imino groups; amide groups; sulfonyl groups; ester groups; ether groups, etc. Groups that combine these groups may also be used.

It is preferable to use a dye having an anionic group. Specific examples of dyes include azo, triphenylmethane, (aza)phthalocyanine, xanthene, and anthrapyridone dyes. A single type of dye may be used alone, or two or more types may be used in combination. The coloring material is preferably a pigment, and more preferably a resin-dispersed pigment or a self-dispersed pigment.

Examples of the anionic groups mentioned in the description of the resin dispersant, self-dispersing pigment, and dye include carboxylic acid groups, sulfonic acid groups, and phosphonic acid groups. The anionic group may be either an acid type or a salt type, and if it is a salt type, it may be either a partially dissociated state or a completely dissociated state. When the anionic group is a salt type, examples of the cation that serves as the counter ion include alkali metal cations, ammonium, and organic ammonium. The coloring material contained in the ink is preferably a pigment, and more preferably a resin-dispersed pigment or a self-dispersed pigment. Of these, it is preferable that the ink contains a resin-dispersed pigment.

(resin)
The ink may contain a resin. The content (mass %) of the resin in the ink is preferably from 0.1% by mass to 20.0% by mass, and more preferably from 0.5% by mass to 15.0% by mass, based on the total mass of the ink.

The resin can be added to the ink (i) to stabilize the dispersion state of the pigment, that is, as a resin dispersant or its auxiliary. Also, (ii) to improve various properties of the recorded image. Examples of the resin form include block copolymers, random copolymers, graft copolymers, and combinations of these. Also, the resin may be a water-soluble resin that can be dissolved in an aqueous medium, or may be resin particles that are dispersed in an aqueous medium. The resin may be used alone or in combination of two or more types.

[Resin Composition]
Examples of the resin include acrylic resins, urethane resins, olefin resins, etc. Among them, acrylic resins and urethane resins are preferred, and acrylic resins composed of units derived from (meth)acrylic acid or (meth)acrylate are more preferred.

As the acrylic resin, one having a hydrophilic unit and a hydrophobic unit as constituent units is preferred. Among them, a resin having a hydrophilic unit derived from (meth)acrylic acid and a hydrophobic unit derived from at least one monomer selected from the group consisting of a monomer having an aromatic ring and a (meth)acrylic acid ester monomer is preferred. In particular, a resin having a hydrophilic unit derived from (meth)acrylic acid and a hydrophobic unit derived from at least one monomer selected from the group consisting of styrene and α-methylstyrene is preferred. These resins are prone to interact with pigments, and can therefore be suitably used as resin dispersants for dispersing pigments.

The hydrophilic unit is a unit having a hydrophilic group such as an anionic group. The hydrophilic unit can be formed, for example, by polymerizing a hydrophilic monomer having a hydrophilic group. Specific examples of hydrophilic monomers having a hydrophilic group include acidic monomers having a carboxylic acid group such as (meth)acrylic acid, itaconic acid, maleic acid, and fumaric acid, and anionic monomers such as anhydrides and salts of these acidic monomers. Examples of cations constituting the salts of acidic monomers include ions of lithium, sodium, potassium, ammonium, and organic ammonium. The hydrophobic unit is a unit that does not have a hydrophilic group such as an anionic group. The hydrophobic unit can be formed, for example, by polymerizing a hydrophobic monomer that does not have a hydrophilic group such as an anionic group. Specific examples of hydrophobic monomers include monomers having an aromatic ring such as styrene, α-methylstyrene, and benzyl (meth)acrylate; and (meth)acrylic acid ester monomers such as methyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate.

Urethane-based resins can be obtained, for example, by reacting polyisocyanate with polyol. They may also be obtained by further reacting with a chain extender. Examples of olefin-based resins include polyethylene and polypropylene.

[Resin properties]
In this specification, "a resin is water-soluble" means that when the resin is neutralized with an alkali equivalent to the acid value, the resin is present in an aqueous medium in a state in which no particles whose particle size can be measured by a dynamic light scattering method are formed. Whether or not a resin is water-soluble can be determined according to the following method. First, a liquid (resin solid content: 10 mass%) containing a resin neutralized with an alkali (sodium hydroxide, potassium hydroxide, etc.) equivalent to the acid value is prepared. Next, the prepared liquid is diluted 10 times (volume basis) with pure water to prepare a sample solution. Then, when the particle size of the resin in the sample solution is measured by a dynamic light scattering method, if no particles having a particle size are measured, the resin can be determined to be water-soluble. The measurement conditions at this time can be, for example, SetZero: 30 seconds, number of measurements: 3 times, and measurement time: 180 seconds. In addition, as a particle size distribution measurement device, a particle size analyzer using a dynamic light scattering method (for example, the product name "UPA-EX150", manufactured by Nikkiso) can be used. Of course, the particle size distribution measurement device and measurement conditions used are not limited to those described above.

The acid value of the water-soluble resin is preferably 100 mgKOH/g or more and 250 mgKOH/g or less. The weight average molecular weight of the water-soluble resin is preferably 3,000 or more and 15,000 or less.

The acid value of the resin constituting the resin particles is preferably 5 mgKOH/g or more and 100 mgKOH/g or less. The weight average molecular weight of the resin constituting the resin particles is preferably 1,000 or more and 3,000,000 or less, more preferably 100,000 or more and 3,000,000 or less. The volume-based cumulative 50% particle diameter (D ₅₀ ) of the resin particles measured by dynamic light scattering is preferably 50 nm or more and 500 nm or less. The volume-based cumulative 50% particle diameter of the resin particles is the diameter of the particles that is 50% of the total volume of the measured particles when integrated from the small particle diameter side in the particle diameter integration curve. The volume-based cumulative 50% particle diameter of the resin particles can be measured using the dynamic light scattering particle size analyzer and measurement conditions described above. The glass transition temperature of the resin particles is preferably 40°C or more and 120°C or less, more preferably 50°C or more and 100°C or less. The glass transition temperature (° C.) of the resin particles can be measured using a differential scanning calorimeter (DSC). The resin particles do not necessarily contain a coloring material.

(Aqueous medium)
The ink is an aqueous ink containing at least water as an aqueous medium. The ink may contain water or an aqueous medium that is a mixed solvent of water and a water-soluble organic solvent. As the water, deionized water or ion-exchanged water is preferably used. The content (mass%) of water in the aqueous ink is preferably 50.0 mass% or more and 95.0 mass% or less based on the total mass of the ink. The content (mass%) of the water-soluble organic solvent in the aqueous ink is preferably 2.0 mass% or more and 45.0 mass% or less based on the total mass of the ink. As the water-soluble organic solvent, any of those usable for inkjet inks, such as alcohols, (poly)alkylene glycols, glycol ethers, nitrogen-containing compounds, and sulfur-containing compounds, can be used. The water-soluble organic solvent may be used alone or in combination of two or more. The water-soluble organic solvent does not include "surfactants".

[Water-soluble hydrocarbon compounds]
The water-soluble organic solvent contained in the ink preferably contains a specific water-soluble hydrocarbon compound. This water-soluble hydrocarbon compound is a compound having a hydrocarbon chain with three or more carbon atoms substituted with two or more hydrophilic groups selected from the group consisting of hydroxyl groups, amino groups, and anionic groups. However, the hydrocarbon chain may be interrupted by a sulfonyl group or an ether group. When the hydrocarbon chain has three or four carbon atoms, the hydrophilic group contains an anionic group, or the hydrocarbon chain is interrupted by a sulfonyl group.

In the present invention, a hydrocarbon compound that is dissolved in water at 25°C at the content of the compound in the ink is considered to be "water-soluble". In other words, the solubility in water at 25°C is greater than the content in the ink. The fact that the hydrocarbon chain is interrupted by a sulfonyl group or an ether group means that a sulfonyl group (-S(=O) ₂ -) or an ether group (-O-) is present in the middle of the hydrocarbon chain. Water-soluble hydrocarbon compounds have hydrogen-bonding groups such as hydroxyl groups, amino groups, anionic groups, sulfonyl groups, and ether groups. Therefore, by using an ink containing this hydrocarbon compound, cockling and curling of a recording medium on which an image is recorded can be suppressed. General hydrocarbon compounds having a hydrocarbon chain with a relatively small number of carbon atoms (3 or 4) tend to have a small molecular weight and a low vapor pressure. However, since the above water-soluble hydrocarbon compounds have anionic groups of hydrogen bonds or the hydrocarbon chain is interrupted by a sulfonyl group, they are difficult to evaporate due to intermolecular or intramolecular interactions, and remain between fibers to suppress cockling and curling. The content (mass %) of the water-soluble hydrocarbon compound in the ink is preferably 1.0 mass % or more and 20.0 mass % or less based on the total mass of the ink.

The number of carbon atoms in the hydrocarbon chain constituting the water-soluble hydrocarbon compound is preferably 3 to 50, and more preferably 3 to 10. Examples of anionic groups include sulfonic acid groups and carboxylic acid groups. Specific examples of water-soluble hydrocarbon compounds include alkanediols such as 1,5-pentanediol and 1,6-hexanediol; amino acids such as alanine, β-alanine, trimethylglycine, amidosulfuric acid (also known as sulfamic acid), aminomethanesulfonic acid, taurine (also known as 2-aminoethanesulfonic acid), carbamic acid, glycine, aspartic acid, glutamic acid, sulfanilic acid, or salts of the above-mentioned acids, phenylalanine, leucine, isoleucine, threonine, tryptophan, valine, methionine, lysine, and arginine; sulfonyl compounds such as bis(2-hydroxyethyl)sulfone; alkylene glycols such as triethylene glycol, tetraethylene glycol, tripropylene glycol, and polyethylene glycols having a number average molecular weight of about 200 to 1,000; and sugars such as sorbitol, D-sorbitol, xylitol, trehalose, fructose, and D(+)-xylose. The water-soluble hydrocarbon compounds may be used alone or in combination of two or more.

(Other ingredients)
In addition to the above components, the ink may contain various additives, such as antifoaming agents, surfactants, pH adjusters, viscosity adjusters, rust inhibitors, preservatives, antifungal agents, antioxidants, reduction inhibitors, etc. However, it is preferable that the ink does not contain a reactant used in the reaction liquid described below.

(Physical properties of ink)
The ink is an aqueous ink applied to the inkjet method. Therefore, from the viewpoint of reliability, it is preferable to appropriately control the physical property values. Specifically, the static surface tension of the ink at 25°C is preferably 20 mN/m or more and 60 mN/m or less. From the viewpoint of making the wax uniformly present on the recording medium and suppressing the change in glossiness at a high level when the ink is fixed, the static surface tension of the ink at 25°C is more preferably 35 mN/m or less. In particular, the static surface tension of the ink is particularly preferably 25 mN/m or more and 35 mN/m or less. In addition, the viscosity of the ink at 25°C is preferably 1.0 mPa·s or more and 10.0 mPa·s or less. The pH of the ink at 25°C is preferably 7.0 to 9.5 or less, more preferably 8.0 to 9.5 or less.

<Reaction solution>
The recording method of the present invention preferably further comprises a reaction liquid application step of applying an aqueous reaction liquid containing a reactant that reacts with the aqueous ink to the recording medium prior to the ink application step. Each component used in the reaction liquid will be described in detail below.

(Reactant)
The reaction liquid reacts with the ink when it comes into contact with the ink, and aggregates the components in the ink (components having anionic groups such as resins, dispersants for dispersing wax, and self-dispersing pigments), and contains a reaction agent. When the reaction agent is present, the state of existence of the components having anionic groups in the ink can be destabilized when the ink and the reaction agent come into contact with each other on the recording medium, and the aggregation of the ink can be promoted. Examples of the reaction agent include cationic components such as polyvalent metal ions and cationic resins, and organic acids. The reaction agent may be used alone or in combination of two or more.

Examples of polyvalent metal ions constituting the polyvalent metal salt include divalent metal ions such as Ca2 ⁺ , Cu2 ⁺ , Ni2 ⁺ , Mg2 ⁺ , Sr2 ⁺ , Ba2 ⁺ , and Zn2 ⁺ , and trivalent metal ions such as Fe3 ⁺ , Cr3 ⁺ , Y3 ⁺ , and Al3 ⁺ . In order to incorporate polyvalent metal ions into the reaction solution, a water-soluble polyvalent metal salt (which may be a hydrate) formed by combining a polyvalent metal ion with an anion can be used. Examples of the anion include inorganic anions such as Cl ⁻ , Br ⁻ , I ⁻ , ClO ⁻ , ClO ₂ ⁻ , ClO ₃ ⁻ , ClO ₄ ⁻ , NO ₂ ⁻ , NO ₃ ⁻ , SO ₄ ²⁻ , CO ₃ ²⁻ , HCO ₃ ⁻ , PO ₄ ³⁻ , HPO ₄ ²⁻ , and H ₂ PO ₄ ⁻ ; and organic anions such as HCOO ⁻ , (COO ⁻ ) ₂ , COOH(COO ⁻ ), CH ₃ COO ⁻ , CH ₃ CH(OH)COO ⁻ , C ₂ H ₄ (COO ⁻ ) ₂ , C ₆ H ₅ COO ⁻ , C ₆ H ₄ (COO ⁻ ) ₂ , and CH ₃ SO ₃ ^{− .} When a polyvalent metal ion is used as a reactant, the content (mass%) of the polyvalent metal salt in the reaction solution is preferably 1.0 mass% or more and 20.0 mass% or less based on the total mass of the reaction solution. In this specification, when the polyvalent metal salt is a hydrate, the "content (mass%) of the polyvalent metal salt in the reaction solution means the "content (mass%) of the anhydride of the polyvalent metal salt" excluding water as the hydrate.

The reaction liquid containing an organic acid has a buffering ability in the acidic range (less than pH 7.0, preferably pH 2.0 to 5.0), and thus efficiently converts the anionic groups of the components present in the ink into the acid form and causes them to aggregate. Examples of organic acids include monocarboxylic acids and their salts, such as formic acid, acetic acid, propionic acid, butyric acid, benzoic acid, glycolic acid, lactic acid, salicylic acid, pyrrole carboxylic acid, furan carboxylic acid, picolinic acid, nicotinic acid, thiophene carboxylic acid, levulinic acid, and coumaric acid; dicarboxylic acids and their salts and hydrogen salts, such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, maleic acid, fumaric acid, itaconic acid, sebacic acid, phthalic acid, malic acid, and tartaric acid; tricarboxylic acids and their salts and hydrogen salts, such as citric acid and trimellitic acid; and tetracarboxylic acids and their salts and hydrogen salts, such as pyromellitic acid. When an organic acid is used as a reactant, the content (mass %) of the organic acid in the reaction solution is preferably 1.0 mass % or more and 50.0 mass % or less based on the total mass of the reaction solution.

Examples of cationic resins include resins having a primary to tertiary amine structure and resins having a quaternary ammonium salt structure. Specific examples include resins having structures such as vinylamine, allylamine, vinylimidazole, vinylpyridine, dimethylaminoethyl methacrylate, ethyleneimine, guanidine, diallyldimethylammonium chloride, and alkylamine-epichlorohydrin condensates. In order to increase the solubility in the reaction solution, the cationic resin can be used in combination with an acidic compound or the cationic resin can be subjected to a quaternization treatment. When a cationic resin is used as a reactant, the content (mass %) of the cationic resin in the reaction solution is preferably 0.1 mass % or more and 10.0 mass % or less based on the total mass of the reaction solution.

(Aqueous medium)
The reaction liquid is an aqueous reaction liquid containing at least water as an aqueous medium. Examples of the aqueous medium used in the reaction liquid include the same aqueous medium as that which can be contained in the ink described above. The content (mass%) of the water-soluble organic solvent in the reaction liquid is preferably 1.0 mass% or more and 45.0 mass% or less based on the total mass of the reaction liquid. The water-soluble organic solvent preferably contains the specific water-soluble hydrocarbon compound described above. The content (mass%) of the water-soluble hydrocarbon compound in the reaction liquid is preferably 1.0 mass% or more and 20.0 mass% or less based on the total mass of the reaction liquid. In addition, the content (mass%) of water in the reaction liquid is preferably 50.0 mass% or more and 95.0 mass% or less based on the total mass of the reaction liquid.

(Other ingredients)
The reaction liquid may contain various other components as necessary. Examples of the other components include the same components as those that can be contained in the ink described above. However, it is preferable that the reaction liquid does not contain wax.

(Properties of reaction solution)
The reaction liquid is an aqueous reaction liquid applied to the inkjet method. Therefore, from the viewpoint of reliability, it is preferable to appropriately control the physical property values. Specifically, the surface tension of the reaction liquid at 25°C is preferably 20 mN/m or more and 60 mN/m or less. In addition, the viscosity of the reaction liquid at 25°C is preferably 1.0 mPa·s or more and 10.0 mPa·s or less. The pH of the reaction liquid at 25°C is preferably 5.0 or more and 9.5 or less, more preferably 6.0 or more and 9.0 or less.

<Inkjet recording method and inkjet recording apparatus>
An inkjet recording method according to one embodiment of the present invention and an inkjet recording apparatus suitable for use in the inkjet recording method will be described below with reference to the drawings. The inkjet recording method of this embodiment is a method for ejecting the above-mentioned ink from an inkjet recording head to record an image on a recording medium. The inkjet recording apparatus of this embodiment is an apparatus equipped with the above-mentioned ink and an inkjet recording head that ejects the ink.

Figure 1 is a schematic diagram showing an example of the general configuration of an inkjet recording device 100 of this embodiment. The inkjet recording device 100 is an inkjet recording device that records an image on a recording medium using ink and a reaction liquid containing a reactant that reacts with the ink. Here, an example will be described in which a reaction liquid is used together with the ink, but a reaction liquid does not have to be used. The X direction, Y direction, and Z direction respectively indicate the width direction (total length direction), depth direction, and height direction of the inkjet recording device. The recording medium is transported in the X direction.

The inkjet recording device 100 of the embodiment shown in FIG. 1 is configured with a recording unit 1000, a heating unit 2000, a fixing unit 3000, and a paper discharge unit 4000. In the recording unit 1000, various liquids are applied by a liquid application device 1200 to the recording medium 1100 conveyed from the paper feed device 1400 by a conveying member 1300. In the heating unit 2000, the liquid components of the image formed by the liquid applied to the recording medium 1100 are heated by the heating device 2100 to evaporate and dry. In the fixing unit 3000, the fixing member 3100 is brought into contact with the area including the image on the recording medium 1100 to heat the image and promote the fixing of the image to the recording medium 1100. Thereafter, the recording medium 1100 is conveyed by the conveying member 4100 of the paper discharge unit 4000 and is stacked and accommodated in the recording medium accommodation unit 4200. Here, an example is described in which the heating unit 2000 and the fixing unit 3000 are included, but depending on the printing conditions (such as the type of ink and printing medium, and printing speed), the heating unit and the fixing unit may be omitted. In the examples described below, printing was performed without using the heating unit 2000 and the fixing unit 3000.

Any recording medium may be used as the recording medium 1100. For example, a recording medium having ink absorption (permeability) such as a recording medium without a coating layer, such as plain paper, uncoated paper, or synthetic paper, or a recording medium with a coating layer, such as glossy paper or art paper, may be used. A recording medium without permeability, such as a film or sheet formed of a resin material, such as polyvinyl chloride (PVC) or polyethylene terephthalate (PET), may be used. The basis weight (g/ ^m2 ) of the recording medium 1100 is preferably 30 g/ ^m2 or more and 500 g/ ^m2 or less, and more preferably 50 g/ ^m2 or more and 450 g/ ^m2 or less.

(Recording section)
The recording unit 1000 includes a liquid applying device 1200. The liquid applying device 1200 includes a reaction liquid applying device 1201 and an ink applying device 1202. The reaction liquid applying device 1201 shown in FIG. 1 is an example of a unit using an inkjet type ejection head. In addition, the reaction liquid applying device may be configured using a gravure coater, an offset coater, a die coater, a blade coater, or the like. The reaction liquid may be applied by the reaction liquid applying device 1201 either before or after the ink application as long as it can come into contact with the ink on the recording medium 1100. However, in order to record high-quality images on various recording media having different liquid absorption characteristics, it is preferable to apply the reaction liquid before the ink is applied. As the ink applying device 1202, an inkjet type ejection head (recording head) is used. The ejection method of the ejection head as the liquid applying device 1200 includes a method of ejecting liquid by generating film boiling in the liquid by an electrothermal converter to form bubbles, and a method of ejecting liquid by an electromechanical converter. Among them, it is preferable to use a recording head that ejects water-based ink by the action of thermal energy. Such a recording head is also called a thermal head. When water-based ink containing wax or resin particles is used in a thermal head, problems tend to occur in terms of ejection stability, but the configuration of the present invention is preferable because it can suppress the occurrence of the above problems.

The liquid application device 1200 is a line head extending in the Y direction, with ejection ports arranged in a range that covers the image recording area of the widest usable recording medium. The ejection head has an ejection port surface (not shown) on its lower side (the recording medium 1100 side) where the ejection ports are formed, and the ejection port surface faces the recording medium 1100 at a very small distance of about a few millimeters.

A plurality of ink applicators 1202 may be provided to apply ink of each color to the recording medium 1100. For example, when recording images of each color using yellow ink, magenta ink, cyan ink, and black ink, four ink applicators 1202 ejecting the above four types of ink are arranged in the X direction. Hereinafter, the ink and reaction liquid may be collectively referred to as "liquid."

Figure 2 is a perspective view showing an example of a liquid application device. The liquid application device 1200 shown in Figure 2 is a line head, and multiple ejection element substrates 1203 each having an ejection port array are arranged in a straight line. Multiple ejection port arrays are arranged on the ejection element substrate 1203.

[Transport system]
As shown in FIG. 1, the recording unit 1000 is configured to include a liquid applying device 1200 and a conveying member 1300 that conveys the recording medium 1100. The liquid applying device 1200 applies a reaction liquid and ink to a desired position of the recording medium 1100 conveyed by the conveying member 1300. Each liquid applying device receives an image signal of drawing data and applies the necessary reaction liquid and ink to each position. FIG. 1 shows the conveying member 1300 in the form of a conveying belt, but a spur, a conveying cylinder, or the like may be used as long as it has the function of conveying the recording medium 1100. In order to improve the conveying accuracy, a material that can fix the recording medium 1100 can be used as the conveying member 1300. Specifically, a method of providing a hole in the conveying member 1300 and fixing the recording medium 1100 by sucking from the back side, a method of forming the conveying member 1300 from an appropriate material and fixing the recording medium 1100 by electrostatic adsorption, etc. can be mentioned.

(Heating section)
As shown in Fig. 1, the heating section 2000 is configured to include a heating device 2100 and a transport member 2200. The recording medium 1100, to which the reaction liquid and ink have been applied and an image has been recorded, is heated by the heating device 2100 while being transported by the transport member 2200, thereby evaporating and drying the liquid components of the image. It is preferable to further include a drying step between the ink application step and the fixing step, in which the recording medium to which the ink has been applied is heated in a non-contact manner to dry the ink. By including such a drying step, deformation (cockling and curling) of the recording medium 1100 can be effectively suppressed.

The heating device 2100 may have any configuration as long as it can heat the recording medium 1100, and various conventional devices such as hot air dryers and heaters can be used. Among these, the use of non-contact heaters such as electric heating wires and infrared heaters is preferable from the standpoint of safety and energy efficiency. In addition, the drying efficiency can be easily improved by using a mechanism that incorporates a fan to spray heated gas onto the recording medium 1100 and blows hot air.

The method of heating may be from the side of the recording medium 1100 to which the reaction liquid and ink have been applied, from the back side, or from both sides. The transport member 2200 may be provided with a heating function. FIG. 1 shows the transport member 2200 in the form of a transport belt, but a spur, transport drum, or the like may also be used as long as it has the function of transporting the recording medium 1100.

(Fixing part)
As shown in FIG. 1, the fixing unit 3000 conveys the recording medium 1100 by the conveying member 3200, and also brings the fixing member 3100 into contact with the recording medium 1100 under pressure, thereby heating the liquid such as the reaction liquid or ink applied to the recording medium 1100. This allows an image to be fixed on the recording medium 1100. From the recording medium 1100 on which an image has been recorded, the liquid components of the reaction liquid or ink permeate the recording medium 1100 or evaporate by passing through the heating unit 2000, and then the image is fixed in the fixing unit 3000, completing the image. By heating and pressurizing the recording medium 1100 while sandwiching it between the fixing member 3100 and the conveying member 3200, the image of the recording medium 1100 and the fixing member 3100 come into close contact with each other, and the image is fixed on the recording medium. When a liquid such as ink containing resin particles and coloring material is used, the resin particles are softened and formed into a film mainly by heating by the fixing unit 3000, and the coloring material can be bound onto the recording medium 1100.

Methods for heating the fixing member 3100 include a method in which a heat source such as a halogen heater is provided inside the roller that drives the fixing member 3100 as a fixing belt, and heating is performed. Also, a method in which a heat source such as an infrared heater is provided in a location separate from the fixing member 3100 and heating is performed can be used. Furthermore, these methods may be combined.

(Paper ejection section)
The recording medium 1100 after the image recording is accommodated in the paper discharge unit 4000 ( FIG. 1 ). Specifically, the recording medium 1100 on which the recording has been performed is transported by a transport member 4100, and is finally accommodated in a stacked state in the recording medium accommodation unit 4200. Two or more recording medium accommodation units 4200 may be provided in order to accommodate different recorded matters, respectively.

The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited in any way to the following examples as long as it does not deviate from the gist of the invention. Unless otherwise specified, the terms "parts" and "%" used to describe the amounts of components are based on mass.

<Preparation of reaction solution>
The components (unit: %) shown in Table 1 were mixed and thoroughly stirred, and then pressure filtered through a cellulose acetate filter (manufactured by Advantec) with a pore size of 3.0 μm to prepare each reaction solution. In Table 1, "Catiomaster PDT-2" is the trade name of an amine-epichlorohydrin condensation polymer aqueous solution (cationic resin content: 60.0%) manufactured by Yokkaichi Chemicals. Also, in Table 1, "Acetylenol E100" is the trade name of a surfactant manufactured by Kawaken Chemicals.

<Preparation of Pigment Dispersion>
(Pigment Dispersion 1)
1.5 g of 4-aminophthalic acid was added to a solution of 5.0 g of concentrated hydrochloric acid in 5.5 g of ion-exchanged water while cooling to 5°C. Next, the container containing this solution was placed in an ice bath and stirred to keep the solution at 10°C or less, and a solution of 0.9 g of sodium nitrite dissolved in 9.0 g of ion-exchanged water at 5°C was added to this. After stirring this solution for another 15 minutes, 6.0 g of pigment (carbon black) was added under stirring. Then, stirring was continued for another 15 minutes. The obtained slurry was filtered with filter paper (product name: standard filter paper No. 2; manufactured by Advantec), and the particles were thoroughly washed with water and dried in an oven at 110°C. Thereafter, sodium ions were replaced with potassium ions by ion exchange to prepare a self-dispersing pigment in which _two -C ₆ H ₄ -(COOK) groups were bonded to the surface of the pigment particles. An appropriate amount of ion-exchanged water was added to this to obtain pigment dispersion 1. The content of the pigment (carbon black) in Pigment Dispersion 1 was 20.0%.

(Pigment Dispersion 2)
A self-dispersing pigment was prepared in the same manner as in the preparation method of the above-mentioned pigment dispersion 1, except that the pigment was changed to C.I. Pigment Blue 15:3, and an appropriate amount of ion-exchanged water was added to obtain a pigment dispersion 2 having a pigment (C.I. Pigment Blue 15:3) content of 20.0%.

(Pigment Dispersion 3)
A styrene-ethyl acrylate-acrylic acid copolymer (resin 1) with an acid value of 150 mgKOH/g and a weight average molecular weight of 8,000 was prepared. 20.0 parts of resin 1 were neutralized with potassium hydroxide in an amount equimolar to the acid value, and then an appropriate amount of pure water was added to prepare an aqueous solution of resin 1 with a resin (solid content) content of 20.0%. 10.0 parts of pigment (C.I. Pigment Blue 15:3), 15.0 parts of the aqueous solution of resin 1, and 75.0 parts of pure water were mixed to obtain a mixture. The obtained mixture and 200 parts of zirconia beads with a diameter of 0.3 mm were placed in a batch-type vertical sand mill (manufactured by Imex) and dispersed for 5 hours while cooling with water. After removing coarse particles by centrifugation, the mixture was pressure-filtered with a cellulose acetate filter (manufactured by Advantec) with a pore size of 3.0 μm. In this manner, Pigment Dispersion Liquid 3 was prepared, which had a pigment (C.I. Pigment Blue 15:3) content of 20.0% and a resin dispersant (Resin 1) content of 10.0%.

(Pigment Dispersion 4)
The pigment used in the preparation of pigment dispersion 3 was changed to a solid solution pigment of C.I. Pigment Violet 19 and C.I. Pigment Red 122. Otherwise, a pigment dispersion 4 having a pigment content of 20.0% (solid solution pigment of C.I. Pigment Violet 19 and C.I. Pigment Red 122) and a resin dispersant content of 10.0% (resin 1) was prepared in the same procedure as in the preparation method of pigment dispersion 3 described above.

(Pigment Dispersion 5)
Except for changing the pigment to C.I. Pigment Red 150, the same procedure as in the preparation method of the pigment dispersion 3 described above was used to prepare a pigment dispersion 5 having a pigment (C.I. Pigment Red 150) content of 20.0% and a resin dispersant (Resin 1) content of 10.0%.

(Pigment Dispersion 6)
A pigment dispersion 6 having a pigment (C.I. Pigment Yellow 74) content of 20.0% and a resin dispersant (Resin 1) content of 10.0% was prepared in the same manner as in the preparation method of the pigment dispersion 3 described above, except that the pigment was changed to C.I. Pigment Yellow 74.

(Pigment Dispersion 7)
Pigment dispersion 7 was prepared using the same procedure as for preparing pigment dispersion 3 described above, except that the pigment was changed to carbon black. The pigment dispersion 7 had a pigment (carbon black) content of 20.0% and a resin dispersant (resin 1) content of 10.0%.

<Preparation of dispersant>
As dispersants for dispersing wax, the following dispersants 1 to 16 were prepared. The "EO number" and "PO number" in the following nonionic dispersants represent the number of moles of ethylene oxide and propylene oxide added (number of repeating units), respectively.
Dispersant 1: Nonionic dispersant; polyoxypropylene butyl ether (PO number 4, HLB value 11.5)
Dispersant 2: Nonionic dispersant; polyoxypropylene cetyl ether (PO number 10, HLB value 10.0)
Dispersant 3: Nonionic dispersant; polyoxyethylene cetyl ether (EO number 8, HLB value 11.9)
Dispersant 4: Nonionic dispersant; polyoxyethylene cetyl ether (EO number 10, HLB value 12.9)
Dispersant 5: Nonionic dispersant; polyoxyethylene cetyl ether (EO number 20, HLB value 15.7)
Dispersant 6: Nonionic dispersant; polyoxyethylene oleyl ether (EO number 30, HLB value 16.6)
Dispersant 7: Nonionic dispersant; polyoxyethylene behenyl ether (EO number 20, HLB value 14.6)
Dispersant 8: Nonionic dispersant; polyoxyethylene behenyl ether (EO number 6, HLB value 9.0)
Dispersant 9: Nonionic dispersant; polyoxyethylene cetyl ether (EO number 4, HLB value 8.4)
Dispersant 10: Nonionic dispersant; polyoxyethylene cetyl ether (EO number 50, HLB value 18.0)
Dispersant 11: Nonionic dispersant; polyoxyethylene myristyl ether (EO number 50, HLB value 18.2)
Dispersant 12: Anionic dispersant; polyoxyethylene alkyl ether sulfate (product name "Newcol 2320-SN", manufactured by Nippon Nyukazai Co., Ltd.)
Dispersant 13: Anionic dispersant; polyoxyethylene alkyl ether phosphate (product name "NIKKOL DDP-8", manufactured by Nikko Chemicals)
Dispersant 14: Anionic dispersant; potassium montanate Dispersant 15: Anionic dispersant; isomerized linoleic acid (linoleic acid having a conjugated structure, CAS number: 67701-06-8)
Dispersant 16: Anionic dispersant; ethylene acrylic acid copolymer

(Method of preparing dispersant 16)
A copolymer of ethylene and acrylic acid was synthesized by a conventional method, neutralized with a neutralizing agent in an amount equimolar to the acid value, and ion-exchanged water was dried under reduced pressure to obtain a solid dispersant 16. The acid value of dispersant 16 was 120 mg KOH/g and the weight average molecular weight was 8,000.

<Preparation of aqueous dispersion of wax particles>
The components (unit: parts) shown in Table 2 (Tables 2-1 to 2-3) were mixed, and the temperature and pressure were appropriately adjusted to disperse the wax, preparing a wax dispersion having a predetermined particle size. Then, an appropriate amount of pure water was added to prepare aqueous dispersions 1 to 32 of wax particles, each having a total content of wax and dispersant of 35.0%. However, aqueous dispersion 30 was prepared without containing wax. Details of wax particles 1 to 4 in Table 2 are shown below.
Wax particle 1: Polyethylene wax (melting point: 90°C)
Wax particles 2: oxidized polyethylene wax (melting point: 100°C)
Wax particles 3: Fischer-Tropsch wax (melting point: 90° C.)
Wax particles 4: Paraffin wax (melting point: 70°C)

<Ink Preparation>
Each component (unit: %) shown in the middle of Table 3 (Tables 3-1 to 3-5) was mixed and thoroughly stirred, and then pressure filtered using a cellulose acetate filter (manufactured by Advantec) with a pore size of 3.0 μm to prepare each ink. The aqueous dispersion of wax particles used was that shown in the upper part of Table 3. The lower part of Table 3 shows the static surface tension (mN/m) of the ink at 25° C. as an ink characteristic. Also shown are the total content (%) of wax and dispersant, wax content A (%), nonionic dispersant content B (%), anionic dispersant content C (%), (B+C)/A value (times), and C/B value (times) based on the total mass of the ink.

<Evaluation>
The reaction liquid applying device 1201 and the ink applying device 1202 of the inkjet recording device 100 having the configuration shown in FIG. 1 were filled with the reaction liquid (see Table 1) and the ink (see Table 3) of the types shown in Table 4. When the reaction liquid was not applied, the reaction liquid applying device 1201 was not filled with the reaction liquid. When the reaction liquid was applied to the recording medium using the inkjet recording device 100, a solid image of 1.6 cm×10 cm was recorded on the recording medium with a reaction liquid recording duty of 7.5% and an ink recording duty of 75%. When the reaction liquid was not applied to the recording medium, a solid image of 1.6 cm×10 cm was recorded on the recording medium with an ink recording duty of 75%. The time difference between the application of the reaction liquid and the application of the ink was adjusted to 100 milliseconds by adjusting the operating speed of the transport member 1300. Coated paper (product name "OK Topcoat+", manufactured by Oji Paper Co., Ltd.) was used as the recording medium. In this example, an image recorded under the condition that four ink droplets of 4.0 ng are applied to a unit area of 1/600 inch x 1/600 inch is defined as having a recording duty of 100%. In this example, in the evaluation criteria for each item below, "AA", "A" and "B" were defined as acceptable levels, and "C" was defined as an unacceptable level. The evaluation results are shown in the evaluation column of Table 4. In Comparative Example 3, in the evaluation of gloss change described below, the solid image peeled off from the recording medium after rubbing, so evaluation of gloss change was not performed and "-" was entered in the gloss change column of Table 4.

(Suppression of changes in glossiness)
Ten minutes after the completion of recording, an unrecorded recording medium (the same recording medium (white background) as that used for recording) and a weight with a surface pressure of 80 g/ ^cm2 were placed on the recorded solid image, and the recorded solid image and the white recording medium were rubbed against each other five times. After that, the white recording medium and the weight were removed, and the solid image was visually observed, and the change in gloss of the image was evaluated according to the following evaluation criteria.
AA: No change in gloss of solid image occurred.
A: A change in glossiness of a solid image occurred, but it was 5% or less of the entire solid image.
B: A change in glossiness of a solid image occurred, but the change was more than 5% and 50% or less of the entire solid image.
C: Changes in gloss of solid images occurred in more than 50% of the entire solid images, which was at a problematic level.

(Abrasion resistance)
The recorded image was left for 1 hour in an environment of 25°C and relative humidity of 55%, and then the surface of the recorded image was rubbed five times with a load of 80 g using a friction resistance tester (product name "AB-301", manufactured by Tester Sangyo), which is a friction tester II (Gakushin type) conforming to JIS L0849. A recording medium of the same type as the recording medium on which the image was recorded was attached to the friction element as a recording paper for evaluation. The surfaces of the image and the recording paper for evaluation after rubbing were visually observed, and the abrasion resistance of the image was evaluated according to the evaluation criteria shown below.
AA: The image was fixed on the recording medium, the white background of the recording medium was not visible, and there was no stain on the recording paper for evaluation.
A: The image was fixed on the recording medium and the white background of the recording medium was no longer visible. After one rub, the evaluation recording paper was not stained. However, after five rubs, the evaluation recording paper was stained.
B: The image was fixed on the recording medium and the white background of the recording medium was no longer visible, but after one rub, the evaluation recording paper was stained.
C: The image was peeled off from the recording medium, revealing the white background of the recording medium.

The disclosure of this embodiment includes the following configurations and methods.
(Configuration 1) A water-based inkjet ink containing a wax, (i) a nonionic dispersant for dispersing the wax, and (ii) an anionic dispersant,
The nonionic dispersant is a compound represented by the following general formula (1) and has an HLB value of 9.0 or more and 18.0 or less,
The aqueous ink according to claim 1, wherein the anionic dispersant is a compound having at least one anionic group selected from the group consisting of a sulfonic acid group, a carboxylic acid group, and a phosphoric acid group.
R ¹ -O-(R ² O) _n -H ... (1)
(In the general formula (1), ^R1 represents an alkyl group or an alkenyl group having 4 or more and 40 or less carbon atoms. Each ^R2 independently represents an ethylene group, a propylene group, or a butylene group. n represents the number of moles of alkylene oxide added and is 3 or more and 50 or less.)
(Configuration 2) The aqueous ink according to configuration 1, wherein the nonionic dispersant is a compound represented by the following general formula (2):
R ¹ -O-(C ₂ H ₄ O) _n -H ... (2)
(In the general formula (2), ^R1 represents an alkyl group or an alkenyl group having 4 or more and 40 or less carbon atoms. n represents the number of moles of alkylene oxide added and is 3 or more and 50 or less.)
(Arrangement 3) The aqueous ink according to Arrangement 1 or 2, wherein the anionic group in the anionic dispersant is a carboxylic acid group.
(Arrangement 4) The aqueous ink according to any one of Arrangements 1 to 3, wherein the number of moles of alkylene oxide added in the nonionic dispersant is 10 or more.
(Configuration 5) An aqueous ink described in any one of Configurations 1 to 4, wherein the total content (mass %) of the nonionic dispersant and the anionic dispersant in the aqueous ink is 0.15 to 0.50 times the mass content (mass %) of the wax.
(Arrangement 6) An aqueous ink described in any one of Arrangements 1 to 5, wherein the content (mass %) of the anionic dispersant in the aqueous ink is 0.10 times or more and 0.50 times or less in mass relative to the content (mass %) of the nonionic dispersant.
(Arrangement 7) The aqueous ink according to any one of Arrangements 1 to 6, wherein the anionic dispersant is an ethylene acrylic acid copolymer.
(Configuration 8) An aqueous ink described in any one of Configurations 1 to 7, wherein the total content (mass %) of the wax, the nonionic dispersant, and the anionic dispersant in the aqueous ink is 0.50 mass % or more and 9.00 mass % or less, based on the total mass of the ink.
(Arrangement 9) The aqueous ink according to any one of Arrangements 1 to 8, further comprising a resin-dispersed pigment.
(Arrangement 10) The aqueous ink according to any one of Arrangements 1 to 9, having a static surface tension (mN/m) of 35 mN/m or less.
(Method 1) An inkjet recording method for recording an image on a recording medium by ejecting ink from an inkjet recording head, comprising the steps of:
11. An ink-jet recording method, wherein the ink is the aqueous ink described in any one of configurations 1 to 10.
(Method 2) The ink jet recording method according to Method 1, wherein the recording head is a recording head that ejects the water-based ink by the action of thermal energy.
(Configuration 11) An inkjet recording apparatus including an ink and an inkjet recording head for ejecting the ink,
11. An ink-jet recording apparatus, wherein the ink is a water-based ink as described in any one of configurations 1 to 10.

Claims (13)

1. A water-based inkjet ink comprising a wax, (i) a nonionic dispersant for dispersing the wax, and (ii) an anionic dispersant,
The nonionic dispersant is a compound represented by the following general formula (1) and has an HLB value of 9.0 or more and 18.0 or less,
The aqueous ink according to claim 1, wherein the anionic dispersant is a compound having at least one anionic group selected from the group consisting of a sulfonic acid group, a carboxylic acid group, and a phosphoric acid group.
R ¹ -O-(R ² O) _n -H ... (1)
(In the general formula (1), ^R1 represents an alkyl group or an alkenyl group having 4 or more and 40 or less carbon atoms. Each ^R2 independently represents an ethylene group, a propylene group, or a butylene group. n represents the number of moles of alkylene oxide added and is 3 or more and 50 or less.) 2. The aqueous ink according to claim 1, wherein the nonionic dispersant is a compound represented by the following general formula (2):
R ¹ -O-(C ₂ H ₄ O) _n -H ... (2)
(In the general formula (2), ^R1 represents an alkyl group or an alkenyl group having 4 or more and 40 or less carbon atoms. n represents the number of moles of alkylene oxide added and is 3 or more and 50 or less.) The aqueous ink according to claim 1, wherein the anionic group in the anionic dispersant is a carboxylic acid group. The aqueous ink according to claim 1, wherein the number of moles of alkylene oxide added in the nonionic dispersant is 10 or more. The aqueous ink according to claim 1, wherein the total content (mass%) of the nonionic dispersant and the anionic dispersant in the aqueous ink is 0.15 to 0.50 times the mass content (mass%) of the wax. The aqueous ink according to claim 1, wherein the content (mass%) of the anionic dispersant in the aqueous ink is 0.10 to 0.50 times the content (mass%) of the nonionic dispersant in the aqueous ink. The aqueous ink according to claim 1, wherein the anionic dispersant is an ethylene acrylic acid copolymer. The aqueous ink according to claim 1, wherein the total content (mass%) of the wax, the nonionic dispersant, and the anionic dispersant in the aqueous ink is 0.50 mass% or more and 9.00 mass% or less based on the total mass of the ink. The aqueous ink according to claim 1, further comprising a resin-dispersed pigment. The aqueous ink according to claim 1, which has a static surface tension (mN/m) of 35 mN/m or less. An inkjet recording method for recording an image on a recording medium by ejecting ink from an inkjet recording head, comprising:
An ink-jet recording method, wherein the ink is a water-based ink according to claim 1 . The inkjet recording method according to claim 11, wherein the recording head is a recording head that ejects the water-based ink by the action of thermal energy. An inkjet recording apparatus including an ink and an inkjet recording head that ejects the ink,
11. An ink jet recording apparatus, wherein the ink is a water-based ink according to claim 1.

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