CN117903627A - Aqueous ink, ink jet recording method, and ink jet recording apparatus - Google Patents

Abstract

The present invention relates to an aqueous ink, an inkjet recording method, and an inkjet recording apparatus. Provided is an aqueous ink for inkjet capable of recording images which have abrasion resistance required in commercial printing and industrial printing and which are suppressed in change in gloss when recorded matter is loaded and their recording surfaces rub against each other. The aqueous ink for inkjet contains a wax, (i) a nonionic dispersant for dispersing the wax, and (ii) an anionic dispersant for dispersing the wax. The nonionic dispersant is a compound represented by the 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.

Description

Aqueous ink, ink jet recording method, and ink jet recording apparatus

Technical Field

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

Background

The inkjet recording method is capable of recording on various recording media. In addition, in order to obtain more satisfactory images, various inks have been proposed according to their uses, such as an ink suitable for recording photographic quality images on glossy paper, for example, and an ink suitable for recording documents on plain paper, for example.

In recent years, the market has demanded that inkjet recording is performed not only on dedicated recording media used so far, such as plain paper or glossy paper for inkjet, but also on paper used so far for offset printing (e.g., coated paper, uncoated paper, or printing paper). In other words, commercial printing and industrial printing in which offset printing has become the mainstream have strong demands for development of inkjet technology that excels in printing in a large variety of small quantities.

In this case, high abrasion resistance, which is comparable to offset printing, is beginning to be demanded while the demand for image quality is far exceeding that of conventional inkjet recording.

For example, in japanese patent application laid-open No.2015-199788, a technique including adding a water-soluble resin to ink to improve abrasion resistance of an image is proposed, and in japanese patent application laid-open No.2018-53124, a technique including aggregating and fixing ink by using a reaction liquid together with the ink is proposed. Further, in each of japanese patent application laid-open No.2010-155359 and japanese patent application laid-open No.2019-203044, a technique including adding wax to ink or a reaction liquid to improve slidability, thereby improving abrasion resistance of an image is proposed.

Disclosure of Invention

The inventors of the present invention have studied whether the methods described in japanese patent application laid-open No.2015-199788, japanese patent application laid-open No.2018-53124, japanese patent application laid-open No.2010-155359, and japanese patent application laid-open No.2019-203044 each provide an image having abrasion resistance comparable to offset printing required in recent years.

The inventors have found that it is difficult to obtain an image having the same level of abrasion resistance as offset printing by the method described in japanese patent application laid-open No. 2015-199788. This is due to the fact that the ink layer is easily peeled off when rubbed with a strong force, because such coated paper used in offset printing does not have any fixing layer unlike ink-jet dedicated paper.

Furthermore, the method described in japanese patent application laid-open No. 2018-53124 has not yet reached the abrasion resistance of images required in offset printing paper.

Furthermore, the inventors have revealed that the methods described in Japanese patent application laid-open No.2010-155359 and Japanese patent application laid-open No.2019-203044 each cause another problem. That is, in each of commercial printing and industrial printing, a recorded image (hereinafter also referred to as "recorded matter") may be loaded in a superimposed manner. At this time, the recording surface of one recorded matter and the recording surface of another recorded matter loaded to face the previous recorded matter or a portion (non-recorded portion) on which no image is recorded rub against each other. The inventors have recognized a new problem in that, as a result of the foregoing, the respective gloss of the recording surfaces is changed to move the recorded matter to a level unacceptable as a recorded matter.

Accordingly, an object of the present invention is to provide an aqueous ink for inkjet capable of recording an image of: the image has abrasion resistance required in commercial printing and industrial printing, and when recorded matter is loaded and their recording surfaces rub against each other, changes in gloss feel of the image are suppressed. Further, another object of the present invention is to provide an inkjet recording method and an inkjet recording apparatus each using an aqueous ink.

That is, according to the present invention, there is provided an aqueous ink for inkjet, comprising a wax, (i) a nonionic dispersant for dispersing the wax, and (ii) an anionic dispersant for dispersing the wax, wherein the nonionic dispersant comprises 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 wherein the anionic dispersant comprises 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:

R¹-O-(R²O)_n-H(1)

In the general formula (1), R ¹ represents an alkyl group or an alkenyl group, and the number of carbon atoms thereof is 4 or more and 40 or less, R ² each independently represents an ethyl group, a propyl group or a butyl group, and "n" represents the number of addition moles of the alkylene oxide, and represents 3 or more and 50 or less.

Other features of the present invention will become apparent from the following description of exemplary embodiments with reference to the accompanying drawings.

Drawings

Fig. 1 is a schematic diagram for illustrating an inkjet recording apparatus according to an embodiment of the present invention.

Fig. 2 is a perspective view for illustrating an example of the liquid applying apparatus.

Detailed Description

The invention is described in more detail below by means of exemplary embodiments. In the present invention, when the compound is a salt, the salt exists in the ink as a dissociative ion, but the expression "containing a salt" is used for convenience. In addition, the aqueous ink and the reaction liquid for inkjet are sometimes simply referred to as "ink" and "reaction liquid". Physical property values are values at room temperature (25 ℃) unless otherwise specified. Description "(meth) acrylic" and "(meth) acrylate" refer to "acrylic or methacrylic" and "acrylate or methacrylate", respectively. In the present invention, "unit" for forming a resin means a repeating unit derived from one monomer.

First, the inventors of the present invention have studied the abrasion resistance of an image in a recorded matter in detail. When performing inkjet recording on paper used in offset printing, the introduction of wax into the ink is one of the requirements required for improving the image abrasion resistance.

Here, when the wax is added to the aqueous ink for inkjet, it is necessary to impart proper dispersibility thereof in an aqueous medium. The method for imparting dispersibility is not particularly limited. The person skilled in the art can impart dispersibility of the wax in an aqueous medium by using known methods. Details about this method will be described later.

The inventors of the present invention studied the abrasion resistance of images by adding various waxes (hereinafter sometimes simply referred to as "waxes") each imparting dispersibility thereof in an aqueous medium to an inkjet ink. As a result, the inventors have concluded that the abrasion resistance of the image can reach the level required in recent years, independently of the kind of dispersant used to impart the respective dispersibility to the wax.

Furthermore, the inventors of the present invention have made more rigorous evaluations than assuming that recorded matter is obtained by offset printing. Specifically, the following tests were performed: performing inkjet recording on a recording medium; the other recording medium is brought into close contact with the recording surface of the preceding medium, and the recording media are rubbed against each other. As a result, the inventors found that the gloss of the recording surface may vary depending on the kind and amount of the dispersant for imparting the dispersibility to each of the waxes. In particular, the inventors have found that when an anionic dispersant is used alone or a nonionic dispersant is used alone, the change in gloss of the recording surface is remarkable. The inventors have studied this phenomenon in more detail and speculated that the reason thereof is as follows.

[ Cause of change in gloss ]

First, the inventors of the present invention studied in detail about the case of dispersing wax by using an anionic dispersant alone. The aqueous ink to which wax is added is applied to a recording medium by an inkjet recording method to record an image, thereby producing a recorded matter. The resultant recorded matter and another recording medium are brought into close contact with each other and rubbed against each other. As a result, the glossiness of the recording surface of the preceding medium varies. According to the study made by the inventors of the present invention, the phenomenon described below may occur in a portion where the gloss feel is changed.

The wax may exhibit the behavior described below on the recording surface of the aqueous ink recorded thereon. When the ink was fixed on the recording medium without any receiving layer, the wax was observed to exist in a state protruding from the ink layer of the recording medium with a Scanning Electron Microscope (SEM). The foregoing is not distinguished from the fact that the slidability of the surface of a recorded matter made with an ink containing wax is improved, and thus the abrasion resistance thereof reaches a desired level.

Meanwhile, when another recording medium is in close contact with the wax protruding from the surface of the ink layer at a position facing the recording surface, and the particles and the recording medium rub against each other, the following event may occur. That is, the upper portion of the wax is rubbed against another recording medium to be shaved off. Thus, the upper portion enters a flat state. The flat surface is in a state of reflecting a large amount of incident light, and may thus vary in gloss.

Further, in the wax using the anionic dispersant, it is presumed that the change in gloss is remarkable for the reasons described below. For example, when the anionic dispersant is a carboxylate, the carboxylate exhibits its dispersibility in an aqueous medium in an ionized state. More specifically, the following is conceivable: the anionic dispersant is ionized; the moiety having a positive charge interacts with the wax and the moiety having a negative charge interacts with the aqueous medium; the wax thus shows a stable dispersed state.

However, the anionic dispersant interacts with a plurality of waxes at one time due to its characteristics, and thus the waxes are fixed in a state of being close to each other. It can be said that the wax easily has a state in which particles are close to each other, in other words, easily has a sea-island structure on the recording medium. The inventors of the present invention speculate that the following are causes of the change in gloss feel becoming evident: in the state where the wax has a sea-island structure, the respective upper portions of the wax are shaved off, and enter a state where a large amount of incident light is reflected as described above.

Next, the inventors of the present invention have also studied the case of dispersing wax using a nonionic dispersant alone. The dispersion stability of the wax dispersed with the nonionic dispersant may be slightly lowered as compared with the case of the anionic dispersant. The inventors have found that the positions where the waxes each having reduced dispersion stability are present on the recording surface of the recording medium are liable to be unevenly distributed. That is, the wax may tend to have a sea-island structure, and it is presumed that as a result, when the nonionic dispersant is used alone, the glossiness of the recording surface also changes.

[ Cause of being able to suppress change in gloss ]

The inventors of the present invention have found that both abrasion resistance of an image and suppression of variation in gloss feel thereof can be achieved using an ink containing a wax dispersed by using a specific nonionic dispersant and a specific anionic dispersant in combination. The inventors of the present invention speculate that the reason is as follows.

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 anionic dispersant. Further, a compound having an HLB value of 9.0 or more and 18.0 or less, which is represented by the general formula (1), is used as the nonionic dispersant. This compound is commonly referred to as a "polyoxyalkylene alkyl ether" or "polyoxyalkylene alkenyl ether". As described above, by using these specific nonionic dispersants and anionic dispersants in combination, the dispersed wax is present on the surface of the recorded matter in a state protruding from the surface of the recorded matter, and thus the sliding property of the surface can be ensured.

R¹-O-(R²O)_n-H(1)

In the general formula (1), R ¹ represents an alkyl group or an alkenyl group, and the number of carbon atoms thereof is 4 or more and 40 or less, R ² each independently represents an ethylene group, a propylene group or a butylene group, "n" represents the number of addition moles of the alkylene oxide, and represents 3 or more and 50 or less.

Further, regarding the change in the gloss of an image, it is presumed that the presence of the specific nonionic dispersant realizes the following state.

When only an anionic dispersant is used as a dispersant for dispersing waxes, the anionic dispersant interacts with a plurality of waxes at once to establish a state in which the waxes are close to each other, so-called sea-island structure. In contrast, when the above specific nonionic dispersant is used in combination with an anionic dispersant, the waxes are difficult to approach each other, and thus it is difficult to have a sea-island structure. Specifically, since the polyoxyalkylene moiety in the molecular structure of the specific nonionic dispersant is present in the vicinity of the wax, the proximity between waxes occurring by the anionic dispersant can be suppressed. In other words, the wax may exist in a state dispersed in the recording surface of the image without being excessively close to each other.

As a result, the change in the gloss of an image due to the fact that the wax is in close contact with and rubbed against the recording medium may be insignificant because the wax has little sea-island structure on the recorded matter even when the wax itself is shaved to have a flat surface, thereby increasing the amount of reflected light, and is therefore dispersed in the recording surface. As a result, the change in gloss can be suppressed.

Furthermore, the inventors of the present invention have found that such effects as described below are also obtained as secondary effects. That is, when a wax dispersed by using the above-described specific nonionic dispersant and anionic dispersant in combination is used, the wax can be caused to exist while being dispersed in the surface of the recording. Studies conducted by the inventors of the present invention have revealed that, as a result of the foregoing, the sliding properties produced by wax are not unevenly distributed in the recording surface, but are uniform to move the abrasion resistance of the image to a higher level. Further studies by the present inventors have found that the above-described effects are not obtained even if a compound corresponding to the above-described nonionic dispersant is added to an ink containing a wax dispersed with an anionic dispersant, or even if a compound corresponding to the above-described anionic dispersant is added to an ink containing a wax dispersed with a nonionic dispersant. In other words, in the present invention, it is important to use a wax dispersed with both a specific nonionic dispersant and an anionic dispersant.

As described above, the nonionic dispersant has an HLB value of 9.0 to 18.0. When the HLB value is set within the above range, the hydrophilicity and hydrophobicity of the nonionic dispersant can be well balanced to suppress the proximity between waxes occurring through the anionic dispersant. When the HLB value deviates from the above range (less than 9.0 or more than 18.0), the balance between the hydrophilicity and the hydrophobicity of the nonionic dispersant is lost, making it difficult for the nonionic dispersant to exist in the vicinity of the wax. Therefore, the approach between waxes cannot be suppressed. Details about the HLB value will be described later.

(Ink)

The ink of the present invention is an aqueous ink for inkjet containing particles (wax particles) formed of wax, the wax particles being wax dispersed with both a specific nonionic dispersant and an anionic dispersant. Each component to be used in ink or the like will be described in detail later.

(Wax particles)

The ink includes wax particles obtained by dispersing a wax with both a nonionic dispersant and an anionic dispersant. Wax particles are particles formed from wax. In other words, the ink contains a wax, a nonionic dispersant for dispersing the wax, and an anionic dispersant for dispersing the wax. The term "wax" as used herein may refer to a composition blended with components other than wax, or may refer to the wax itself.

Waxes are esters of higher monohydric or dihydric alcohols and fatty acids which are narrowly insoluble in water. Thus, animal-based waxes and vegetable-based waxes are included in the category of waxes, but oils and fats are not included therein. Broadly included are blends and modifications of high melting point fats, mineral waxes, petroleum waxes, and various waxes. In the recording method of the present invention, waxes in a broad sense may each be used without any particular limitation. The broad wax can be classified into natural wax, synthetic wax, blends thereof (blended wax), and modifications thereof (modified wax).

Examples of natural waxes may include: animal waxes such as beeswax, spermaceti and lanolin; vegetable-based waxes such as japan wax, carnauba wax, sugarcane wax, palm wax, candelilla wax, and rice wax; mineral-based waxes such as montan wax; and petroleum-based waxes such as paraffin wax, microcrystalline wax, and vaseline. Examples of the synthetic wax may include hydrocarbon-based waxes such as Fischer-Tropsch wax and polyolefin wax (e.g., polyethylene wax and polypropylene wax). The blended wax is a mixture of the various waxes described above. The modified wax is obtained by subjecting the above-mentioned various waxes to a modification treatment such as oxidation, hydrogenation, alcohol modification, acrylic modification or urethane modification. For example, oxidized polyolefin is a product obtained by subjecting polyolefin to an oxidation treatment. Oxidized polyolefins may be synthesized by oxidizing polyolefins or commercially available products may be used. Examples of such oxidized polyolefin may include oxidized polyethylene wax and oxidized polypropylene wax, which are oxidation products of polyolefin wax. The waxes described above may be used alone or in combination thereof. The wax is preferably at least one selected from the group consisting of: microcrystalline wax; fischer-Tropsch wax; polyolefin wax; paraffin wax; and modified products and blends thereof. Among these, a blend of a plurality of waxes is more preferable, and a blend of petroleum wax and synthetic wax is particularly preferable.

The wax is preferably solid at room temperature (25 ℃). The melting point (. Degree.C.) of the wax is preferably 40℃or more and 120℃or less, more preferably 50℃or more and 100℃or less. The melting point of the wax may be in accordance with JIS K2235: 1991 (Petroleum wax) section 5.3.1 (melting point test method). In the case of microcrystalline waxes, petrolatum and mixtures of waxes, their melting points can be measured with greater accuracy by using the test method described in section 5.3.2 thereof. The melting point of waxes is susceptible to characteristics such as molecular weight (a larger molecular weight provides a higher melting point), molecular structure (a linear structure provides a higher melting point, while a branched structure provides a lower melting point), crystallinity (a higher crystallinity provides a higher melting point), and density (a higher density provides a higher melting point). Thus, controlling these properties can provide a wax having a desired melting point. The melting point of the wax in the ink can be measured, for example, as follows: after washing and drying of the wax classified by subjecting the ink to ultracentrifugation treatment, the melting point thereof was measured according to each of the above-described test methods.

The content (mass%) of the wax in the ink is preferably 0.30 mass% or more and 8.00 mass% or less, more preferably 0.50 mass% or more and 4.00 mass% or less, relative to the total mass of the ink. The total content (mass%) of the wax and the dispersant for dispersing the wax in the ink is preferably 0.50 mass% or more and 10.00 mass% or less, preferably 0.50 mass% or more and 9.00 mass% or less, more preferably 1.00 mass% or more and 5.00 mass% or less, relative to the total mass of the ink. The dispersant for dispersing the wax contains (i) a nonionic dispersant and (ii) an anionic dispersant described later.

(Dispersant for wax)

[ Nonionic dispersant ]

The compound represented by the following general formula (1) is used as a nonionic dispersant for dispersing wax. Such compounds are sometimes referred to as "polyoxyalkylene alkyl ethers" or "polyoxyalkylene alkenyl ethers". For convenience, alkyl ethers and alkenyl ethers are hereinafter collectively referred to as "alkyl ethers". The nonionic dispersant has an HLB value of 9.0 to 18.0.

R¹-O-(R²O)_n-H

In the general formula (1), R ¹ represents an alkyl group or an alkenyl group, and the number of carbon atoms thereof is 4 or more and 40 or less, R ² each independently represents an ethylene group, a propylene group or a butylene group, and "n" represents the number of addition moles of the alkylene oxide, and represents 3 or more and 50 or less.

R ¹ represents an alkyl group or an alkenyl group, and the number of carbon atoms is 4 or more and 40 or less. R ² each independently represents ethylene, propylene or butylene. Among them, ethylene or propylene is preferable. "n" represents the number of addition moles of the alkylene oxide and is 3 to 50 inclusive.

The "HLB value" of the surfactant used herein is a value determined by the Griffin method, and is calculated based on the equation "HLB value=20× (formula amount of hydrophilic group of surfactant)/(molecular weight of surfactant)". The HLB value determined by the Griffin method is a physical property value indicating the degree of hydrophilicity or lipophilicity of the surfactant, and is 0 to 20. As the HLB value becomes smaller, the lipophilicity becomes higher, and as the HLB value becomes larger, the hydrophilicity becomes higher.

Examples of the polyoxyalkylene alkyl ether may include: polyoxyethylene alkyl ether (formula (2): R ¹-O-(C₂H₄O)_n -H); polyoxypropylene alkyl ether (formula (3): R ¹-O-(C₃H₆O)_n -H); polyoxyethylene-polyoxypropylene alkyl ether (formula (4): R ¹-O-[(C₂H₄O)_n1-(C₃H₆O)_n2 -H); and polyoxybutenyl alkyl ether (formula (5): R ¹-O-(C₄H₈O)_n -H). Among them, polyoxyethylene alkyl ethers and polyoxypropylene alkyl ethers are preferable. These nonionic dispersants may be used alone or in combination. As described above, R ¹ in each of the general formulae (2) to (5) represents an alkyl group or an alkenyl group, and "n" (including n1 and n2 independent of each other) represents the number of addition moles (the number of repeating units) of alkylene oxide (ethylene oxide, propylene oxide or butylene oxide).

Examples of the polyoxyethylene alkyl ether may 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 the polyoxypropylene alkyl ether may include polyoxypropylene butyl ether, polyoxypropylene myristyl ether, polyoxypropylene cetyl ether and polyoxypropylene stearyl ether.

Examples of the polyoxyethylene-polyoxypropylene alkyl ether may 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. That is, the nonionic dispersant is preferably a compound represented by the following general formula (2).

R¹-O-(C₂H₄O)_n-H……(2)

In the general formula (2), R ¹ represents an alkyl group or an alkenyl group, and the number of carbon atoms thereof is 4 or more and 40 or less, and "n" represents the number of addition moles of the alkylene oxide, and represents 3 or more and 50 or less.

When the polyoxyethylene alkyl ether and the anionic dispersant are used in combination for dispersing the wax, uneven distribution of the wax in the recording surface of the recording medium is easily suppressed, thus making the wax more uniformly present on the recording medium. Therefore, the change in gloss of the recording surface can be effectively suppressed.

Further, the number of addition moles of alkylene oxide in the polyoxyalkylene alkyl ether is more preferably 10 or more, because the change in gloss is effectively suppressed. Alkylene oxides may be referred to as, for example, "alkylene oxide", "polyoxyalkylene chain" or "polyalkylene oxide chain". The addition mole number of alkylene oxide is the number of repeating units of ethylene oxide, propylene oxide, butylene oxide or the total number thereof. The addition mole number of the alkylene oxide is preferably 40 or less.

Further, the hydrocarbon group represented by R ¹ in each of the general formulae (2) to (4) may be any one of a linear and branched group, and may be any one of a saturated group and an unsaturated group. The number of carbon atoms of the hydrocarbon group represented by R ¹ is more preferably 5 to 30. When the number of carbon atoms of the hydrocarbon group is 5 or more and 30 or less, interaction between wax particles generated by the anionic dispersant used in combination with the polyoxyalkylene alkyl ether is suppressed, and thus uneven distribution of wax in the recording surface is easily suppressed. Therefore, the change in gloss of the image is easily and effectively suppressed. The number of carbon atoms of the hydrocarbon group represented by R ¹ is particularly preferably 8 to 30.

The nonionic dispersant is preferably a nonionic surfactant. Surfactants are materials composed of a hydrophobic moiety (hydrocarbon chain, perfluoroalkyl, siloxane structure, etc.) and a hydrophilic moiety (e.g., ethylene oxide group). In other words, the nonionic dispersant preferably does not contain a water-soluble organic solvent (e.g., triethylene glycol monobutyl ether (R ¹: 4, n: 3), tetraethylene glycol monobutyl ether (R ¹: 4, n: 3), etc.), even if the compound represented by the general formula (1) is used.

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 mass% or more and 2.50 mass% or less, more preferably 0.10 mass% or more and 2.50 mass% or less, relative to the total mass of the ink. In particular, the content is still more preferably 0.30 mass% or more and 1.50 mass% or less.

[ 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 an anionic dispersant for dispersing wax. In particular, the anionic groups in the anionic dispersant are preferably carboxylic acid groups.

The inventors of the present invention speculate that the reason why the anionic group in the anionic dispersant is preferably a carboxylic acid group is as follows. The anionic dispersant having a carboxylic acid group may form a hydrogen bond directly or through water in the ink and the nonionic dispersant used in combination therewith. As a result, the position of fixation of the wax dispersed with the above-described dispersant can become more random, and therefore the wax hardly has a sea-island structure. It is possible to effectively suppress the change in the gloss of the image as a result of the foregoing.

An anionic surfactant, a resin having an anionic functional group, or the like can be suitably used as the anionic dispersant having an anionic group. Specifically, for example, a carboxylate, sulfonate, sulfate, or phosphate may be used as the anionic surfactant. Examples of the anionic dispersant include straight-chain higher carboxylic acids (salts), sulfonic acids (salts), alkylbenzenesulfonates, alkyl sulfate salts, polyoxyethylene alkyl sulfate salts, alkyl phosphate salts, and resins having anionic functional groups. More specifically, examples of anionic dispersants include montanic acid, isomerized linoleic acid, and salts thereof.

In addition, for example, an ethylene-acrylic acid copolymer can be suitably used as the resin having an anionic functional group. The anionic dispersant having an anionic group is preferably a resin having an anionic group, more preferably an ethylene-acrylic acid copolymer. The use of the ethylene-acrylic acid copolymer improves the dispersibility of the wax while improving the effect exhibited by the combined use of the anionic dispersant and the nonionic dispersant. Thus, uneven distribution of wax in the recording surface is suppressed, and thus variation in gloss can be suppressed at a higher level.

The content (mass%) of the anionic dispersant in the ink is preferably 0.01 mass% or more and 2.50 mass% or less, more preferably 0.02 mass% or more and 2.00 mass% or less, relative to the total mass of the ink. In particular, the content is particularly preferably 0.04% by mass or more and 1.50% by mass or less.

The mass ratio of the total content (mass%) of the nonionic dispersant and the anionic dispersant in the ink to the content (mass%) of the wax therein is preferably 0.15 times or more and 0.50 times or less. When the mass ratio is set to 0.15 times or more, the dispersion stability of the wax is sufficiently obtained, and thus the change in the gloss of an image can be suppressed at a higher level. Meanwhile, when the mass ratio is set to 0.50 times or less, dispersion stability of the wax can be maintained while suppressing sinking of the wax into the recording medium. Therefore, the abrasion resistance of the image can be further improved.

The mass ratio of the content (mass%) of the anionic dispersant in the ink to the content (mass%) of the nonionic dispersant therein is preferably 0.10 times or more and 0.50 times or less. When the above mass ratio is set in the above range, interaction between wax particles generated by the anionic dispersant used in combination with the nonionic dispersant is suppressed while the wax is stably dispersed, and thus uneven distribution of the wax in the surface of the recording medium is easily suppressed. Therefore, the change in gloss of the image can be suppressed at a higher level.

[ Coloring Material ]

The ink preferably comprises a coloured material. Pigments or dyes may be used as coloring materials. The content (mass%) of the coloring material in the ink is preferably 0.5 mass% or more and 15.0 mass% or less, more preferably 1.0 mass% or more and 10.0 mass% or less, relative to the total mass of the ink.

Specific examples of pigments may include: inorganic pigments such as carbon black and titanium oxide; and organic pigments such as azo, phthalocyanine, quinacridone, isoindolinone, imidazolone, diketopyrrolopyrrole and dioxazine pigments. Pigments may be used alone or in combination.

A resin-dispersed pigment using a resin as a dispersant, a self-dispersed pigment having a hydrophilic group bonded to the particle surface thereof, or the like can be used as a dispersion system for pigments. Further, a resin-bonded pigment having a resin-containing organic group chemically bonded to the particle surface thereof, a microcapsule pigment containing particles whose surfaces are covered with, for example, a resin, or the like, may be used. Among these pigments, pigments different from each other in the dispersion system may be used in combination. In the present invention, it is preferable to use a resin-dispersed pigment in which a resin serving as a dispersant is physically adsorbed to the particle surface of the pigment or a self-dispersed pigment having a hydrophilic group bonded to the particle surface thereof, instead of a resin-bonded pigment or a microcapsule pigment.

It is preferable to use a dispersant capable of dispersing a pigment in an aqueous medium by the action of an anionic group as a resin dispersant for dispersing a pigment in an aqueous medium. The resin having an anionic group can be used as a resin dispersant, and such a resin as described below, particularly a water-soluble resin, is preferably used. The mass ratio of the content (mass%) of the pigment in the ink to the content (mass%) of the resin dispersant therein is preferably 0.3 times or more and 10.0 times or less.

Pigments having anionic groups bonded to their particle surfaces either directly or through any other atomic group (-R-), can be used as self-dispersing pigments. Specific examples of other radicals (-R-) may include: a linear or branched alkylene group having 1 to 12 carbon atoms; arylene groups such as phenylene or naphthylene; a carbonyl group; an imino group; an amide group; a sulfonyl group; an ester group; and an ether group. Furthermore, a group obtained by combining these groups can be employed.

Preferably, a dye having an anionic group is used as the dye. Specific examples of the dye may include dyes such as azo dyes, triphenylmethane dyes, (aza) phthalocyanine dyes, xanthene dyes, and anthrapyridone dyes. The dyes may be used alone or in combination thereof. The coloring material is preferably a pigment, more preferably a resin-dispersed pigment or a self-dispersing pigment.

The above anionic groups in the description of the resin dispersant, the self-dispersing pigment and the dye include, for example, carboxylic acid groups, sulfonic acid groups and phosphonic acid groups. The anionic group may be any of an acid type or a salt type. When the group is in a salt form, the group may be in any one of a state in which a part of the group is dissociated or a state in which the whole thereof is dissociated. When the anionic group is in a salt form, examples of cations used as counter ions may include alkali metal cations, ammonium and organic ammonium. The coloring material contained in the ink is preferably a pigment, more preferably a resin-dispersed pigment or a self-dispersed pigment. In particular, the ink preferably contains a resin-dispersed pigment.

[ Resin ]

The resin may be incorporated into the ink. The content (mass%) of the resin in the ink is preferably 0.1 mass% or more and 20.0 mass% or less, more preferably 0.5 mass% or more and 15.0 mass% or less, relative to the total mass of the ink.

A resin may be added to the ink for (i) stabilizing the dispersed state of the pigment, i.e., as a resin dispersant or an auxiliary agent. Further, a resin may be added to the ink for (ii) improving various characteristics of the recorded image. Examples of the resin form may include block copolymers, random copolymers, graft copolymers, and combinations thereof. Further, the resin may be a water-soluble resin that is soluble in an aqueous medium, or may be resin particles dispersed in an aqueous medium. The resins may be used alone or in combination thereof.

[ Composition of resin ]

Examples of the resin may include acrylic resins, urethane resins, and olefin resins. Among them, acrylic resins and urethane resins are preferable, and acrylic resins including units derived from (meth) acrylic acid or (meth) acrylic acid esters are more preferable.

As the acrylic resin, a resin having a hydrophilic unit and a hydrophobic unit as its structural unit is preferable. Among them, a resin having a hydrophilic unit derived from (meth) acrylic acid and a hydrophobic unit derived from at least one selected from the group consisting of a monomer having an aromatic ring and a (meth) acrylic acid ester-based monomer is preferable. Particularly preferred are resins 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. These resins can each be suitably used as a resin dispersant for dispersing pigments because each of these resins easily causes interaction with pigments.

The hydrophilic unit is a unit having a hydrophilic group such as an anionic group. The hydrophilic unit may be formed by, for example, polymerizing a hydrophilic monomer having a hydrophilic group. Specific examples of the hydrophilic monomer having a hydrophilic group may include: acidic monomers each 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. The cation used to form the salt of the acidic monomer may be, for example, lithium, sodium, potassium, ammonium or organic ammonium ions. The hydrophobic unit is a unit that does not contain a hydrophilic group such as an anionic group. The hydrophobic unit may be formed by, for example, polymerizing a hydrophobic monomer that does not contain a hydrophilic group such as an anionic group. Specific examples of the hydrophobic monomer may include: monomers each having an aromatic ring, such as styrene, α -methylstyrene and benzyl (meth) acrylate; and (meth) acrylic ester-based monomers such as methyl (meth) acrylate, butyl (meth) acrylate, and 2-ethylhexyl (meth) acrylate.

The urethane-based resin can be obtained, for example, by reacting a polyisocyanate and a polyol with each other. In addition, a chain extender may be further reacted with the reaction product. Examples of the olefinic resin may include polyethylene and polypropylene.

[ Properties of resin ]

The phrase "the resin is water-soluble" as used herein means that when the resin is neutralized with an amount of an alkali equal to its acid value, the resin is present in an aqueous medium in a state in which the resin does not form any particles whose particle size can be measured by a dynamic light scattering method. Whether the resin is water-soluble or not can be judged according to the following method. First, a liquid (resin solid content: 10 mass%) containing a resin neutralized with a base (for example, sodium hydroxide or potassium hydroxide) corresponding to the acid value thereof is prepared. Next, the prepared liquid was diluted ten times (based on volume) with pure water to prepare a sample solution. Then, when the particle diameter of the resin in the sample solution is measured by the dynamic light scattering method, the particle having the particle diameter is not measured, it can be judged that the resin is water-soluble. The measurement conditions at this time may be set as follows, for example: setZero:30 seconds; number of measurements: 3 times; measuring time: 180 seconds. Further, a particle size analyzer based on a dynamic light scattering method (for example, an analyzer of product name "UPA-EX150" available from Nikkiso co., ltd.) or the like may be used as the particle size distribution measuring device. Of course, the particle size distribution measuring apparatus, the measurement conditions, and the like to be used are not limited to the foregoing.

The acid value of the water-soluble resin is preferably 100mgKOH/g or more and 250mgKOH/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 used to form the resin particles is preferably 5mgKOH/g or more and 100mgKOH/g or less. The weight average molecular weight of the resin used to form 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 50% cumulative particle diameter (D ₅₀) on a volume basis of the resin particles measured by the dynamic light scattering method is preferably 50nm or more and 500nm or less. The 50% cumulative particle diameter on a volume basis of the resin particles is a particle diameter at which the ratio of particles that accumulate from small particle diameters to the total volume of the particles to be measured reaches 50% in the particle diameter cumulative curve. The 50% cumulative particle diameter based on the volume of the resin particles was measured with the particle size analyzer of the dynamic light scattering system described above and under the measurement conditions described above. The glass transition temperature of the resin particles is preferably 40 ℃ or more and 120 ℃ or less, more preferably 50 ℃ or more and 100 ℃ or less. The glass transition temperature (. Degree. C.) of the resin particles can be measured by a Differential Scanning Calorimeter (DSC). The resin particles need not include any coloring material.

[ Aqueous Medium ]

The ink is an aqueous ink including at least water as an aqueous medium. An aqueous medium as water or a mixed solvent of water and a water-soluble organic solvent may be introduced into the ink. Deionized water or ion-exchanged water is preferably used as water. The content (mass%) of water in the aqueous ink is preferably 50.0 mass% or more and 95.0 mass% or less with respect to the total mass of the ink. Further, 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 with respect to the total mass of the ink. Solvents usable for ink-jet inks, such as alcohols, (poly) alkylene glycols, glycol ethers, nitrogen-containing compounds and sulfur-containing compounds, can each be used as a water-soluble organic solvent. The water-soluble organic solvents may be used alone or in combination thereof. The water-soluble organic solvent should not include a "surfactant".

[ Water-soluble Hydrocarbon Compound ]

The water-soluble organic solvent to be incorporated into the ink preferably contains a specific water-soluble hydrocarbon compound. The water-soluble hydrocarbon compound is a compound having a hydrocarbon chain of 3 or more carbon atoms, which is substituted with 2 or more hydrophilic groups each selected from the group consisting of a hydroxyl group, an amino group, and an anionic group. However, the hydrocarbon chain may be interrupted by sulfonyl groups or ether groups. When the number of carbon atoms of the hydrocarbon chain is 3 or 4, the hydrophilic group includes an anionic group or the hydrocarbon chain is interrupted by a sulfonyl group.

In the present invention, the hydrocarbon compound in a state of being dissolved in water at a content of the hydrocarbon compound in the ink at 25 ℃ is defined as "water-soluble". That is, the solubility of the compound in water at 25 ℃ is greater than its content in 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. The water-soluble hydrocarbon compound has hydrogen-binding groups such as hydroxyl groups, amino groups, anionic groups, sulfonyl groups, and ether groups. Therefore, wrinkling or curling of the recording medium on which an image is recorded can be suppressed using the ink containing the hydrocarbon compound. Typical hydrocarbon compounds having hydrocarbon chains with relatively small numbers of carbon atoms (3 or 4 carbon atoms) tend to have small molecular weights and thus low vapor pressures. However, the above-mentioned water-soluble hydrocarbon compound has a hydrogen-binding anionic group or its hydrocarbon chain interrupted by a sulfonyl group. Therefore, the compound is difficult to evaporate due to intermolecular or intramolecular interactions, and thus remains between fibers constituting the recording medium to exhibit an inhibition effect on wrinkling or 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 with respect to the total mass of the ink.

The number of carbon atoms of the hydrocarbon chain for forming the water-soluble hydrocarbon compound is preferably 3 or more and 50 or less, more preferably 3 or more and 10 or less. Examples of the anionic group may include a sulfonic acid group and a carboxylic acid group. Specific examples of the water-soluble hydrocarbon compound may include: alkanediols, such as 1, 5-pentanediol and 1, 6-hexanediol; amino acids such as alanine, beta-alanine, trimethylglycine, amidosulfuric acid (amidosulfuric acid) (alias: sulfamic acid), sulfamic acid, taurine (alias: 2-aminoethanesulfonic acid), carbamic acid, glycine, aspartic acid, glutamic acid, sulfanilic acid or salts of any of the above 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 from about 200 to about 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 thereof.

[ Other Components ]

In addition to the above components, the ink may include various additives such as an antifoaming agent, a surfactant, a pH adjuster, a viscosity modifier, an antirust agent, a preservative, a fungicide, an antioxidant, and an antireductant, as required. However, the ink preferably contains no reactant used in a reaction liquid described later.

[ Physical Properties of ink ]

The ink is an aqueous ink applied to an inkjet system. Therefore, from the viewpoint of reliability, it is preferable to appropriately control the physical property value of the ink. Specifically, the static surface tension of the ink at 25℃is preferably 20mN/m or more and 60mN/m or less. From the viewpoint of uniformly allowing wax to exist on the recording medium at the time of ink fixing to suppress a high level of change in gloss, the static surface tension of the ink at 25 ℃ is more preferably 35mN/m or less, particularly preferably 25mN/m or more and 35mN/m or less. The viscosity of the ink at 25℃is preferably 1.0 mPas or more and 10.0 mPas or less. The pH of the ink at 25 ℃ is preferably 7.0 or more and 9.5 or less, more preferably 8.0 or more and 9.5 or less.

(Reaction liquid)

The recording method of the present invention preferably further includes a reaction liquid application step of applying an aqueous reaction liquid containing a reactant that reacts with the aqueous ink to the recording medium before the ink application step. The respective components used in the reaction liquid and the like are described in detail below.

[ Reactant ]

The reaction liquid is brought into contact with the ink to react with the ink, thereby aggregating components in the ink (such as a resin, a dispersant for dispersing wax, and a self-dispersing pigment, etc., which have an anionic group). The reaction solution contains a reactant. When the reactant is present, the presence state of the component having an anionic group in the ink is unstable upon contact between the ink and the reactant in the recording medium, and thus aggregation of the ink can be promoted. Examples of reactants may include: a multivalent metal ion; cationic components, such as cationic resins; and an organic acid. The reactants may be used alone or in combination thereof.

Examples of the polyvalent metal ion forming the polyvalent metal salt may include: divalent metal ions such as Ca ²⁺、Cu²⁺、Ni²⁺、Mg²⁺、Sr²⁺、Ba²⁺ and Zn ²⁺; and trivalent metal ions such as Fe ³⁺、Cr³⁺、Y³⁺ and Al ³⁺. A water-soluble polyvalent metal salt (may be a hydrate) composed of a polyvalent metal ion and an anion bonded to each other can be used to introduce the polyvalent metal ion into the reaction liquid. Examples of such anions may include: inorganic anions such as Cl^-、Br^-、I^-、ClO^-、ClO₂ ^-、ClO₃ ^-、ClO₄ ^-、NO₂ ^-、NO₃ ^-、SO₄ ^2-、CO₃ ^2-、HCO₃ ^-、PO₄ ^3-、HPO₄ ^2- and H ₂PO₄ ^-; and organic anions such as HCOO^-、(COO^-)₂、COOH(COO^-)、CH₃COO^-、CH₃CH(OH)COO^-、C₂H₄(COO^-)₂、C₆H₅COO^-、C₆H₄(COO^-)₂ and CH ₃SO₃ ^-. When a polyvalent metal ion is used as the reactant, the content (mass%) thereof in the reaction liquid in terms of the polyvalent metal salt is preferably 1.0 mass% or more and 20.0 mass% or less with respect to the total mass of the reaction liquid. In the present specification, when the polyvalent metal salt is a hydrate, "content of the polyvalent metal salt (mass%) in the reaction liquid" means "content of anhydride of the polyvalent metal salt (mass%) obtained by removing water used as the hydrate".

The reaction liquid containing the organic acid has a buffer capacity in an acidic region (pH of less than 7.0, preferably pH of 2.0 to 5.0) to effectively convert anionic groups of components present in the ink into an acid form, thereby aggregating the ink. Examples of the organic acid may include: monocarboxylic acids 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, and salts thereof; dicarboxylic acids 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, and salts and hydrogen salts thereof; tricarboxylic acids such as citric acid and trimellitic acid, and salts and hydrogen salts thereof; and tetracarboxylic acids such as pyromellitic acid and salts and hydrogen salts thereof. When an organic acid is used as the reactant, the content (mass%) of the organic acid in the reaction liquid is preferably 1.0 mass% or more and 50.0 mass% or less with respect to the total mass of the reaction liquid.

Examples of the cationic resin may include resins having a structure of primary to tertiary amines and resins having a structure of quaternary ammonium salts. Specific examples thereof may include resins having structures such as vinylamine, allylamine, vinylimidazole, vinylpyridine, dimethylaminoethyl methacrylate, ethyleneimine, guanidine, diallyldimethylammonium chloride, and alkylamine-epichlorohydrin condensates. In order to improve the solubility in the reaction liquid, a cationic resin and an acidic compound may be used in combination, or the cationic resin may be quaternized. When a cationic resin is used as the reactant, the content (mass%) of the cationic resin in the reaction liquid is preferably 0.1 mass% or more and 10.0 mass% or less with respect to the total mass of the reaction liquid.

[ 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 may include the same ones as those that can be incorporated into the above-described ink. The content (mass%) of the water-soluble organic solvent in the reaction solution is preferably 1.0 mass% or more and 45.0 mass% or less with respect to the total mass of the reaction solution. The water-soluble organic solvent preferably contains the above specific water-soluble hydrocarbon compound. The content (mass%) of the water-soluble hydrocarbon compound in the reaction solution is preferably 1.0 mass% or more and 20.0 mass% or less relative to the total mass of the reaction solution. The content (mass%) of water in the reaction solution is preferably 50.0 mass% or more and 95.0 mass% or less with respect to the total mass of the reaction solution.

[ Other Components ]

The reaction solution may contain various other components as needed. Examples of the other components may include the same ones as those that can be incorporated into the above-described ink. However, the reaction solution preferably contains no wax.

[ Physical Properties of reaction solution ]

The reaction liquid is an aqueous reaction liquid applied to an inkjet system. Therefore, from the viewpoint of reliability, it is preferable to appropriately control the physical property value of the reaction liquid. Specifically, the surface tension of the reaction solution at 25℃is preferably 20mN/m or more and 60mN/m or less. The viscosity of the reaction solution at 25℃is preferably 1.0 mPas or more and 10.0 mPas or less. The pH of the reaction solution at 25℃is preferably 5.0 to 9.5, more preferably 6.0 to 9.0.

< Inkjet recording method and inkjet recording apparatus >

An inkjet recording method and an inkjet recording apparatus that can be suitably used for the inkjet recording method according to one embodiment of the present invention are described below with reference to the drawings. The inkjet recording method of the present embodiment is a method including ejecting the above-described ink from a recording head of an inkjet system to record an image on a recording medium. The ink jet recording apparatus of the present embodiment is provided with the above-described ink and an ink jet recording head for ejecting the ink.

Fig. 1 is a schematic diagram showing an example of a schematic configuration of an inkjet recording apparatus 100 of the present embodiment. The inkjet recording apparatus 100 is an inkjet recording apparatus that records an image on a recording medium with a reactive liquid containing a reactive agent that reacts with ink and ink. Here, description will be made by taking a case where the reaction liquid is used together with ink as an example. However, the reaction liquid may not be used. The X direction, Y direction, and Z direction denote a width direction (total length direction), a depth direction, and a height direction of the inkjet recording apparatus, respectively. The recording medium is conveyed in the X direction.

The inkjet recording apparatus 100 of the embodiment shown in fig. 1 includes: a recording section 1000; a heating unit 2000; a fixing section 3000; a sheet discharge section 4000. In the recording section 1000, various liquids are applied to a recording medium 1100 that has been conveyed from the paper feeding device 1400 by the conveying member 1300 by the liquid applying device 1200. In the heating section 2000, a liquid component of an image formed by a liquid applied to the recording medium 1100 is evaporated and dried by heating with the heating device 2100. In the fixing portion 3000, the fixing member 3100 contacts an area of the recording medium 1100 including an image to heat the image, thereby facilitating 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 section 4000, and is loaded and stored in the recording medium storage section 4200. Here, description is made by taking a configuration including the heating portion 2000 and the fixing portion 3000 as an example. However, depending on the recording conditions (e.g., the kind of ink and recording medium and the recording speed), the heating portion or the fixing portion may be omitted. In the embodiment described later, recording is performed without using the heating portion 2000 and the fixing portion 3000.

Any medium may be used as the recording medium 1100. For example, such recording media each having ink absorbency (permeability) as described below may each be used as the recording medium 1100: recording media without a coating layer, such as plain paper, uncoated paper, or synthetic paper; and a recording medium including a coating layer, such as glossy paper or coated paper. Further, a recording medium having no 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/m ²) of the recording medium 1100 is preferably 30g/m ² or more and 500g/m ² or less, more preferably 50g/m ² or more and 450g/m ² or less.

[ Recording section ]

The recording section 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 ejection head of an inkjet system. The reaction liquid applying means may be formed by using a gravure coater, an offset coater, a die coater, a blade coater, or the like, in addition to the ejection head. The reaction liquid may be applied by the reaction liquid applying device 1201 before the ink is applied, or may be applied after the ink is applied, as long as the liquid can be in 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 applying the ink. An ejection head (recording head) of an inkjet system is used as the ink applying device 1202. Examples of the ejection system serving as the ejection head of the liquid application device 1200 include: a system including a film boiling in a liquid with an electro-thermal transducer to form bubbles, thereby ejecting the liquid; and systems including ejection of liquids with electro-mechanical transducers. Among them, a recording head configured to eject aqueous ink by the action of thermal energy is preferably used. Such a recording head is also called a so-called thermal head. In the thermal head, the use of an aqueous ink containing wax and resin particles is liable to cause problems in ejection stability. However, the thermal head is preferable because the occurrence of the above-described problems can be suppressed with the configuration of the present application.

The liquid applying device 1200 is a line-type head disposed in an extending manner in the Y direction, and its ejection orifices are arranged in a range covering an image recording area of a recording medium having the maximum usable width. The ejection head has an ejection orifice surface (not shown) having ejection orifices formed on its lower side (recording medium 1100 side). The ejection orifice surface faces the recording medium 1100 at a minute distance of about several millimeters.

A plurality of ink applying devices 1202 may be provided for applying the inks of the respective colors to the recording medium 1100. For example, when recording images of respective colors with yellow ink, magenta ink, cyan ink, and black ink, four ink application devices 1202 that eject the above four inks are arranged side by side in the X direction. The ink and the reaction liquid are sometimes collectively referred to as "liquid" hereinafter.

Fig. 2 is a perspective view showing an example of the liquid application device. The liquid applying apparatus 1200 shown in fig. 2 is a line head, and a plurality of ejection element substrates 1203 having an ejection orifice array provided therein are arranged linearly. The ejection element substrates 1203 each have a plurality of ejection orifice arrays arrayed therein.

[ Conveying System ]

As shown in fig. 1, the recording section 1000 includes a liquid applying device 1200 and a conveying member 1300 that conveys a recording medium 1100. The reaction liquid and the ink are applied to a desired position of the recording medium 1100 conveyed by the conveying member 1300 by the liquid applying device 1200. Each liquid applying device receives an image signal of drawing data to apply a desired reaction liquid and ink to each position. Although a conveying member 1300 in the form of a conveying belt is shown in fig. 1, for example, a spur gear (spur) or a conveying roller may be used as long as the spur gear or the conveying roller has a function of conveying the recording medium 1100. A member that can fix the recording medium 1100 can be used as the conveying member 1300 to improve conveying accuracy. Specific examples thereof may include: a method including providing a hole in the conveying member 1300 and attracting the recording medium 1100 from the back side of the recording medium 1100 to fix the medium; and a method including forming the conveying member 1300 from a suitable material and electrostatically adsorbing the recording medium 1100 to fix the medium.

[ Heating portion ]

As shown in fig. 1, the heating part 2000 includes a heating device 2100 and a conveying member 2200. The recording medium 1100 on which an image is recorded by applying the reaction liquid and the ink is heated by the heating device 2100 while being conveyed by the conveying member 2200. Thus, the liquid component of the image evaporates and dries. The recording method preferably further includes a drying step between the ink applying step and the fixing step of subjecting the recording medium to which the ink has been applied to non-contact heating to dry the ink. The presence of such a drying step can effectively suppress deformation (wrinkling or curling) of the recording medium 1100.

The heating device 2100 may have any configuration as long as the device is capable of heating the recording medium 1100. Various conventionally known devices, such as a warm air dryer and a heater, may be used each. Among them, non-contact heaters such as heating wires and infrared heaters are preferably utilized in terms of safety and energy efficiency. In addition, the drying efficiency is easily improved by using the following mechanism: the mechanism has built therein a fan for ejecting heated gas onto the recording medium 1100 and blows warm air thereto.

As for the method for heating, the recording medium 1100 may be heated from the side of the surface to which the reaction liquid and the ink have been applied, may be heated from the back side thereof, or may be heated from both sides. A heating function may be given to the conveying member 2200. Although the conveying member 2200 in the form of a conveying belt is shown in fig. 1, for example, a spur gear or a conveying roller may be used as long as the spur gear or the conveying roller has a function of conveying the recording medium 1100.

[ Fixing portion ]

As shown in fig. 1, in the fixing portion 3000, the recording medium 1100 is conveyed by a conveying member 3200. Further, the fixing member 3100 contacts the recording medium 1100 in a state where the medium is pressurized to heat the liquid, such as the reaction liquid and the ink, applied to the recording medium 1100. Accordingly, the image can be fixed to the recording medium 1100. After the liquid components of the reaction liquid and the ink permeate into the recording medium 1100 on which the image is recorded and they are evaporated from the recording medium 1100 by the heating portion 2000, the reaction liquid and the ink are fixed in the fixing portion 3000 to complete the image. When the recording medium 1100 is heated and pressurized in a state of being sandwiched between the fixing member 3100 and the conveying member 3200, the image on the recording medium 1100 and the fixing member 3100 are in close contact with each other, and thus the image is fixed to the recording medium. When a liquid such as ink containing resin particles and a coloring material is used, the resin particles soften by heating mainly through the fixing portion 3000 to form a film, and thus the coloring material can be bonded to the recording medium 1100.

A method of heating the fixing member 3100 may be, for example, a system including a heat source such as a halogen heater provided inside each roller driving the fixing member 3100 serving as a fixing belt to heat the member. Further, the method may be, for example, a system including a heat source such as an infrared heater provided at a position different from the fixing member 3100 to heat the member. Furthermore, these systems may be combined with each other.

[ Paper discharge portion ]

The recording medium 1100 after image recording is stored in the paper discharge section 4000 (fig. 1). Specifically, the recorded recording medium 1100 is conveyed by the conveying member 4100 to be finally stored in the recording medium storage portion 4200 in the loaded state. More than two recording medium storage parts 4200 may be provided for storing different recorded matters, for example, respectively.

Examples (example)

The present invention will be described in more detail by examples and comparative examples. The present invention is by no means limited to the following examples without departing from the gist of the present invention. Unless otherwise indicated, "parts" and "%" of the description of the amounts of the components are by mass.

< Preparation of reaction solution >

The respective components (unit:%) shown in table 1 were mixed and stirred thoroughly, followed by filtration under pressure with a cellulose acetate filter (manufactured by Advantec) having a pore size of 3.0 μm. Thus, each reaction solution was prepared. In table 1, the term "CATIOMASTER PDT-2" represents the product name of an aqueous amine-epichlorohydrin condensation polymer solution (cationic resin content: 60.0%) manufactured by Yokkaichi Chemical co. The term "ACETYLENOL E" shown in table 1 represents the product name of the surfactant manufactured by KAWAKEN FINE CHEMICALS co.

TABLE 1

Composition of the reaction solution

< Preparation of pigment Dispersion >

(Pigment Dispersion 1)

To a solution obtained by dissolving 5.0g of concentrated hydrochloric acid in 5.5g of ion-exchanged water, 1.5 g of 4-aminophthalic acid was added in a state where the solution was cooled to 5 ℃. Next, the container containing the solution was put into an ice bath, and the solution temperature was maintained below 10 ℃ all the time by stirring the solution. To this solution was added a solution obtained by dissolving 0.9g of sodium nitrite in 9.0g of ion-exchanged water at5 ℃. The resulting solution was further stirred for 15 minutes, and then 6.0g of pigment (carbon black) was added thereto with stirring. After that, the mixture was stirred for a further 15 minutes. The resulting slurry was filtered through filter paper (product name: STANDARD FILTER PAPER No.2; manufactured by Advantec), and the particles were then thoroughly washed with water and then dried in an oven at 110 ℃. Thereafter, the sodium ion is replaced with potassium ion by an ion exchange method to prepare a self-dispersing pigment in which the-C ₆H₄-(COOK)₂ group is bonded to the surface of the pigment particle. An appropriate amount of ion-exchanged water was added to the self-dispersible pigment to provide a pigment dispersion liquid 1. The pigment (carbon black) content in the pigment dispersion liquid 1 was 20.0%.

(Pigment Dispersion liquid 2)

Self-dispersing pigments were prepared by the same procedure as the above-described method for preparing pigment dispersion 1, except that the pigment was changed to c.i. pigment blue 15:3. To the self-dispersing pigment, an appropriate amount of ion-exchanged water was added to provide a pigment dispersion liquid 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) having an acid value of 150mgKOH/g and a weight-average molecular weight of 8,000 was prepared. 20.0 parts of resin 1 was neutralized with potassium hydroxide in a molar amount equal to the acid value, and then an appropriate amount of pure water was added. Thus, an aqueous solution of resin 1 having a resin content (solid content) of 20.0% was prepared. 10.0 parts of pigment (c.i. pigment blue 15:3), 15.0 parts of an aqueous solution of resin 1, and 75.0 parts of pure water were mixed to provide a mixture. The resultant mixture and 200 parts of zirconia beads each having a diameter of 0.3mm were charged into a batch-type vertical sand mill (AIMEX co., manufactured by ltd.) and dispersed for 5 hours while being cooled with water. The dispersed product was centrifuged to remove coarse particles, followed by filtration under pressure with a cellulose acetate filter (manufactured by Advantec) having a pore size of 3.0 μm. Thus, pigment dispersion 3 having a pigment (c.i. pigment blue 15:3) content of 20.0% and a resin dispersant (resin 1) content of 10.0% was prepared.

(Pigment Dispersion 4)

A pigment dispersion 4 having a content of pigment (solid solution pigment of c.i. pigment violet 19 and c.i. pigment red 122) of 20.0% and a content of resin dispersant (resin 1) of 10.0% was produced by the same procedure as the above-described method for producing the pigment dispersion 3, except that the pigment was changed to a solid solution pigment of c.i. pigment violet 19 and c.i. pigment red 122.

(Pigment Dispersion 5)

A pigment dispersion 5 having a content of pigment (c.i. pigment red 150) of 20.0% and a content of resin dispersant (resin 1) of 10.0% was prepared by the same procedure as the above-described method for preparing pigment dispersion 3, except that the pigment was changed to c.i. pigment red 150.

(Pigment Dispersion 6)

A pigment dispersion 6 having a content of pigment (c.i. pigment yellow 74) of 20.0% and a content of resin dispersant (resin 1) of 10.0% was prepared by the same procedure as the above-described method for preparing pigment dispersion 3, except that the pigment was changed to c.i. pigment yellow 74.

(Pigment Dispersion 7)

A pigment dispersion 7 in which the content of pigment (carbon black) was 20.0% and the content of resin dispersant (resin 1) was 10.0% was prepared by the same procedure as the above-described method for preparing pigment dispersion 3, except that the pigment was changed to carbon black.

< Preparation of dispersant >

The following dispersants 1 to 16 were prepared as dispersants for dispersing wax. The terms "EO number" and "PO number" in the following nonionic dispersant refer to the addition mole number (number of repeating units) of ethylene oxide and propylene oxide, respectively. Dispersant 1: a nonionic dispersant; polyoxypropylene butyl ether (PO number: 4, HLB value: 11.5)

Dispersant 2: a nonionic dispersant; polyoxypropylene cetyl ether (PO number: 10, HLB value: 10.0). Dispersant 3: a nonionic dispersant; polyoxyethylene cetyl ether (EO value: 8, hlb value: 11.9). Dispersant 4: a nonionic dispersant; polyoxyethylene cetyl ether (EO value: 10, hlb value: 12.9). Dispersant 5: a nonionic dispersant; polyoxyethylene cetyl ether (EO value: 20, hlb value: 15.7). Dispersant 6: a nonionic dispersant; polyoxyethylene oleyl ether (EO value: 30, hlb value: 16.6) ·dispersant 7: a nonionic dispersant; polyoxyethylene behenyl ether (EO value: 20, HLB value: 14.6). Dispersant 8: a nonionic dispersant; polyoxyethylene behenyl ether (EO value: 6, HLB value: 9.0). Dispersant 9: a nonionic dispersant; polyoxyethylene cetyl ether (EO value: 4, hlb value: 8.4). Dispersant 10: a nonionic dispersant; polyoxyethylene cetyl ether (EO value: 50, hlb value: 18.0). Dispersant 11: a nonionic dispersant; polyoxyethylene myristyl ether (EO value: 50, hlb value: 18.2). Dispersant 12: an anionic dispersant; polyoxyethylene alkyl ether sulfate (product name: newcol2320-SN ", nippon Nyukazai Co., ltd.,

Dispersant 13: an anionic dispersant; polyoxyethylene alkyl ether phosphate (product name: NIKKOL DDP-8", manufactured by Nikko Chemicals Co., ltd.)

Dispersant 14: an anionic dispersant; brown coal acid potassium salt

Dispersant 15: an anionic dispersant; isomerized linoleic acid (linoleic acid with conjugated structure, CAS number: 67701-06-8)

Dispersant 16: an anionic dispersant; ethylene-acrylic acid copolymer

(Method for producing dispersant 16)

Copolymers of ethylene and acrylic acid are synthesized in a conventional manner and neutralized with a neutralizing agent in a molar amount equal to the acid value thereof. Further, ion-exchanged water was evaporated to dryness under reduced pressure. Thus, the solid dispersant 16 was obtained. The acid value of the dispersant 16 was 120mgKOH/g, and the weight-average molecular weight was 8,000.

< Preparation of aqueous dispersion of wax particles >

The components (units: parts) shown in Table 2 (Table 2-1 to Table 2-3) were mixed, followed by appropriately adjusting the temperature and pressure to disperse the wax. Thus, wax dispersions each having a predetermined particle diameter are prepared. Then, an appropriate amount of pure water was added to the dispersion to prepare aqueous dispersions 1 to 32 of wax particles, each of which had a total content of wax particles and dispersant of 35.0%. Aqueous dispersion 30 was prepared without the introduction of wax.

Details about the wax particles 1 to 4 shown in table 2 are described below.

Wax particles 1: polyethylene wax (melting point: 90 ℃ C.)

Wax particles 2: oxidized polyolefin wax (melting point: 100 ℃ C.)

Wax particles 3: fischer-Tropsch wax (melting point: 90 ℃ C.)

Wax particles 4: paraffin (melting point: 70 ℃ C.)

TABLE 2-1

Composition (parts) of aqueous dispersion of wax particles

TABLE 2-2

Composition (parts) of aqueous dispersion of wax particles

Tables 2 to 3

Composition (parts) of aqueous dispersion of wax particles

< Preparation of ink >

The components (units:%) shown in the columns of Table 3 (tables 3-1 to 3-4) were mixed and stirred well, followed by filtration under pressure with a cellulose acetate filter (manufactured by Advantec) having a pore size of 3.0 μm. The product whose number is shown in the upper part of Table 3 is used as an aqueous dispersion of wax particles. The static surface tension (mN/m) of the ink at 25℃is shown as the ink characteristics in the lower part of Table 3. Further, the values (times) of the total content (%) of the wax and the dispersant, the content a (%) of the wax, the content B (%) of the nonionic dispersant, and the content C (%) of the anionic dispersant, and "(b+c)/a" and the values (times) of "C/B" are shown with respect to the total mass of each ink.

TABLE 3-1

Composition and Properties of ink

TABLE 3-2 composition and Properties of ink

TABLE 3-3

Composition and Properties of ink

Tables 3 to 4

Composition and Properties of ink

< Evaluation >

The reaction liquids (see table 1) and inks (see table 3) of the types shown in table 4-1 and table 4-2 were respectively charged into the reaction liquid applying device 1201 and the ink applying device 1202 of the inkjet recording apparatus 100 having the configuration shown in fig. 1. When the reaction liquid is not applied, no reaction liquid is loaded into the reaction liquid applying device 1201. When the reaction liquid was applied to the recording medium with the inkjet recording apparatus 100, a solid image having a size of 1.6cm×10cm, which had a reaction liquid recording job of 7.5% and an ink recording job of 75%, was recorded on the recording medium. When the reaction liquid is not applied to the recording medium with the inkjet recording apparatus 100, a solid image having a size of 1.6cm×10cm, which has a 75% ink recording job, is recorded on the recording medium. By adjusting the operation speed of the conveying member 1300, the time difference from the application of the reaction liquid to the application of the ink was adjusted to 100 milliseconds. Coated Paper (product name: "OKTOP COAT+", manufactured by Oji Paper Co., ltd.) was used as the recording medium.

In the present embodiment, an image recorded under the following conditions is defined as having a recording task of 100%: 4 ink droplets each having a mass of 4.0ng were applied to a unit area having a size of 1/600 inch by 1/600 inch. In the present embodiment, in the respective evaluation criteria of the following items, the levels "AA", "a" and "B" are defined as acceptable levels, and the level "C" is defined as unacceptable levels. The evaluation results are shown in the evaluation columns of Table 4-1 and Table 4-2. In comparative example 3, in the evaluation of the change in gloss described later, after the image and the recording medium are rubbed against each other, the solid image peels off from the recording medium. Therefore, no evaluation of change in gloss was performed, and the symbol "-" is shown in the column of "change in gloss" of table 4-2.

(Inhibition of gloss change)

After 10 minutes from the completion of recording, a recording medium (same recording medium (white background) as used in recording) having no recorded image and a weight having a surface pressure of 80g/cm ² were mounted on the recorded solid image, and then the recorded solid image and the white background recording medium were repeatedly rubbed against each other five times. After that, the white background recording medium and the weight that have been mounted were removed, and the solid image was visually observed, followed by evaluation of the change in gloss of the image according to the following evaluation criteria.

AA: the gloss of the solid image is not changed.

A: the gloss of the solid image was changed, but it was 5% or less of the whole solid image.

B: the gloss of the solid image changes, but it is more than 5% and 50% or less of the whole solid image.

C: the change in gloss of the solid image is at a level that causes problems because such a change occurs in more than 50% of the solid image as a whole.

(Abrasion resistance)

The recorded image was left at 25 ℃ and 55% relative humidity for 1 hour. Thereafter, the surface of the image was friction-recorded five times under a load of 80g in accordance with JIS L0849 using an anti-friction Tester (product name: "AB-301", manufactured by Tester Sangyo Co., ltd.) as friction Tester II (type Gakushin). A recording medium of the same kind as the recording medium on which the image is recorded is stuck as an evaluation recording paper to a block (block) portion. The image surface after the friction test and the surface of the recording paper for evaluation were visually observed, and then the abrasion resistance of the image was evaluated according to the following evaluation criteria.

AA: the image was fixed to the recording medium to prevent the white background of the recording medium from being observed, and no contamination was present on the recording paper for evaluation.

A: the image was fixed to the recording medium to prevent the observation of a white background of the recording medium, and no contamination was present on the recording paper for evaluation at the time point of one rubbing. However, after five rubs, there was contamination on the recording paper for evaluation.

B: the image was fixed to the recording medium to prevent the observation of a white background of the recording medium, but at the point of time when one rubbing was performed, there was contamination on the recording paper for evaluation.

C: the image peels off the recording medium, displaying a white background of the recording medium.

TABLE 4-1

Evaluation conditions and results

TABLE 4-2

Evaluation conditions and results

According to the present invention, it is possible to provide an inkjet aqueous ink capable of recording an image, which has abrasion resistance required in commercial printing and industrial printing, and which suppresses a change in gloss when recorded matter is loaded and their recording surfaces rub against each other. Further, according to the present invention, an inkjet recording method and an inkjet recording apparatus using an aqueous ink can be provided.

While the invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

Claims (13)

1. An aqueous ink for inkjet, characterized in that the aqueous ink contains a wax, (i) a nonionic dispersant for dispersing the wax and (ii) an anionic dispersant for dispersing the wax,

Wherein the nonionic dispersant comprises 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

Wherein the anionic dispersant comprises 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), R ¹ represents an alkyl group or an alkenyl group and has a carbon number of 4 or more and 40 or less, R ² each independently represents an ethylene group, a propylene group or a butylene group, and "n" represents an addition mole number of an alkylene oxide and represents 3 or more and 50 or less.

2. The aqueous ink according to claim 1, wherein the nonionic dispersant comprises a compound represented by the following general formula (2):

R¹-O-(C₂H₄O)_n-H(2)

In the general formula (2), R ¹ represents an alkyl group or an alkenyl group and has a carbon number of 4 or more and 40 or less, and "n" represents an addition mole number of the alkylene oxide and represents 3 or more and 50 or less.

3. The aqueous ink according to claim 1, wherein the anionic group in the anionic dispersant comprises a carboxylic acid group.

4. The aqueous ink according to claim 1, wherein the number of addition moles of alkylene oxide in the nonionic dispersant is 10 or more.

5. The aqueous ink according to claim 1, wherein a mass ratio of a total content in mass% of the nonionic dispersant and the anionic dispersant in the aqueous ink to a content in mass% of the wax in the aqueous ink is 0.15 times or more and 0.50 times or less.

6. The aqueous ink according to claim 1, wherein a mass ratio of a content of the anionic dispersant in mass% to a content of the nonionic dispersant in mass% in the aqueous ink is 0.10 times or more and 0.50 times or less.

7. The aqueous ink according to claim 1, wherein the anionic dispersant comprises an ethylene-acrylic acid copolymer.

8. The aqueous ink according to claim 1, wherein a total content of the wax, the nonionic dispersant, and the anionic dispersant in the ink is 0.50 mass% or more and 9.00 mass% or less in mass%.

9. The aqueous ink according to claim 1, wherein the aqueous ink further comprises a resin-dispersed pigment.

10. The aqueous ink according to claim 1, wherein the static surface tension of the aqueous ink is 35mN/m or less.

11. An inkjet recording method of recording an image onto a recording medium by ejecting ink from an inkjet recording head, characterized in that the ink contains the aqueous ink according to any one of claims 1 to 10.

12. The inkjet recording method according to claim 11, wherein the recording head includes a recording head that discharges the aqueous ink by an action of thermal energy.

13. An inkjet recording apparatus, comprising:

An ink; and

A recording head of an ink jet system configured to eject the ink,

Characterized in that the ink comprises an aqueous ink according to any one of claims 1 to 10.